INTRODUCTION

The recent discovery by a deep-water remotely controlled submersible of the wreck of the German WWII battleship KM BISMARCK has renewed interest in that ship's capabilities vis-a-vis its battleship contemporaries in other navies at the time. This article is an analysis of the armor protection designed into this warship and its capabilities to inflict damage an other armored warships compared with their abilities to damage the BISMARCK.

I am going to compare the BISMARCK to its similar-sized British, American, Japanese French, and Italian battleship contemporaries, launched or actually building in 1941. Thus, I am skipping the U.S. North Carolina class, which were replaced by the South Dakota Class, and am occasionally mentioning the U.S. Iowa class, which are very similar to the South Dakota regarding their armor arrangement.

ARMOR TYPES

The types of armor used on the BISMARCK were similar to that used an contemporary warships, though with some unique features.

HOMOGENEOUS ARMOR

Armor used for horizontal protection (armored decks and turret or conning tower roofs) and for vertical protection from 1-4 inches (25.4-101.6 mm) thick was of a soft, ductile, homogeneous steel manufactured by Krupp and called by the German Navy "Wotan Harte n/A" (Hardened 'Wotan' steel New Type), abbreviated "Wh n/A." Wh was first used in the German cruisers and "Pocket Battleships" of the late 1920's and remained in use through the end of WWII. The steel was a slightly improved form of the original medium-carbon (0.2-0.4 percent carbon) nickel-chromium steel introduced in 1894 by Krupp and later forming the basis of all high-grade armors made of steel even today by all nations. Wh n/A used some molybdenum to improve manufacturing results and was slightly tougher (crack resistant) than the original "High-Percent Nickel-Steel," also called "Krupp Soft" or "Quality 420" (Krupp's own label) steel, used through the end of WWI. Otherwise, there was little to choose from between the older armors and Wh n/A armor. British "Non-Cemented" armor (NCA) and U.S. "Class 'B'" armor or "Special Treatment Steel (STS) were similar materials, to name just a few. My information indicates that WWII U.S. Class 'B' armor was slightly superior to German Wh, though the difference is so slight as to be of little significance compared to all other sources of error during most evaluations.

Homogeneous (the same everywhere inside and out) armor is usually kept soft and ductile, with the hardening (strengthening) kept an high as possible with the restrictions that (1) the armor does not got so hand as to crack prior to the projectile being completely stopped or deflected, if the projectile is rejected, or prior to the last possible moment, if the projectile is going to penetrate anyway; (2) the armor remains in one piece with as few fragments being thrown from it as possible if a hole is made, so that complete penetration of the projectile itself is needed for major damage behind the plate; and (3) the armor does not cause major damage to the impacting projectile at high obliquity where such damage might allow pieces of a broken projectile through a hole it made in the plate, but where an intact projectile would be rejected entirely if it could not fit through that hole. Values of 225-250 on the Brinell hardness scale was the usual range for homogeneous Krupp-steel naval armor (soft wrought iron is roughly 100 and mild steel roughly 120-150 on this same hardness scale).

This form of armor uses its toughness to stay in one piece and continue resisting the projectile for the longest possible time as the projectile causes the plate to bend and stretch and finally tear open entirely through. While projectile damage (especially nose damage) may reduce projectile penetration at low (near right-angles) impact obliquities, at angles of impact above about 45^o from right angles the projectile is "defeated' by causing it to be deflected away like a stone skipping off of the surface of a pool of water. The force on the projectile is caused by the high-leverage push on the nose's side in contact with the plate which forces the projectile to rotate in a direction parallel to the plate's face. At high obliquity, unless the projectile is able to dig into the plate deep enough at the start to be held by the material surrounding it until it can push open a hole entirely through, the projectile nose will tear from the plate and the projectile will ricochet off, leaving a long groove, with or without a slot-like tear at its bottom. As long an the projectile remains in one piece, if the nose glances off, so does the entire projectile (only in extremely thin plates hit at very high velocity can the projectile tear through sideways even if the nose fails to dig in). The blunter the projectile's nose, the less leverage the force has and the more the force decelerates rather than deflects the projectile, so the less effect increasing the impact angle has on the penetration. Also, if the projectile breaks apart, deflection of the nose pieces does not prevent the lower portion of the projectile from pushing on into the plate region already weakened by the stress of deflecting the nose and piercing the plate there, so for projectile deflection rather than deceleration to be fully utilized as a means to keep projectiles out, they must remain in one piece at high obliquity.

The armor-piercing (AP) cap used by most large-caliber armor piercing projectiles since circa 1898 to greatly improve penetration against face-hardened armor causes just the opposite effect against thicker (over about 0.4 times the projectile's diameter in thickness) homogeneous armor at low obliquity (the thicker and harder the cap, the worse the degradation is). The negative effects of using an AP cap against homogeneous armor are much reduced at high obliquity, where the usually blunt cap shape helps the projectile by inhibiting ricochet (but never as helpful as not having a cap and making the projectile nose itself as blunt as the cap face is, though such a blunt nose reduces penetration ability against thick armor at low obliquity).

For plates under 4 inches thick, making extremely high hardness steel armors that damage high-quality AP projectiles at low obliquity ("KC" armors to be discussed below) was difficult to realize reliably during the time frame that we are talking about, so homogeneous steel armor was the best against smaller AP projectiles at all obliquities. When armor plates are inclined, such as is the case for horizontal armor for protection against large ("over-matching") gun projectiles at short to medium ranges where impacts are highly oblique, the use of the deflection effects is critical and homogeneous armor is the only correct choice. This is true for all thicknesses of armor above roughly 45^o obliquity (zero degrees obliquity is right angle -- "normal" -- in my measurement scale).

For plates under about 1 inch (25.4 mm), it is possible to control the hardening process with more reliability and to harden the armor to higher levels without too much loss in toughness (crack resistance). This thickness of armor was designed to resist machinegun fire with lead bullets from strafing aircraft and small fragments of nearby exploding projectiles, not to defeat hardened armor-piercing projectiles. The high hardness allowed added strength while the ability to keep adequate toughness prevented the plates from being holed by punching out plugs of armor (the usual failure mode of brittle materials). As mentioned, for small-caliber solid-shot-type projectiles like machinegun bullets, if the impacting projectile were to be rejected, but the plate itself had pieces punched out of it, those pieces can cause much the same damage that the projectile would have, which means that the armor has accomplished nothing by stopping that projectile (at least in the region immediately behind the plate holed). For this purpose German WWII ships used a Krupp homogeneous armor called "Wotan Starrheit" (Extra-hard 'Wotan') (Wsh) that was similar in composition to Wh n/A but hardened to 250-280 Brinell (at 300 Brinell hardness cracking became a major problem in thicker plates). Many light gun and director shields, including the spherical shields of the BISMARCK's four stabilized anti-aircraft gun directors, used Wsh armor.

For thin plates that made up the BISMARCK's internal anti-torpedo bulkheads, impact by projectiles or fragments was not a concern, but the maximum ability to resist tearing under the water hammer effect of a torpedo or mine hit was paramount. Krupp developed a form of armor called "Wotan Weich" (Soft 'Wotan') (Ww) for these 1.97-inch (50 mm) and less bulkheads that was kept at roughly 200 Brinell, about the softest possible for this kind of steel. However, later tests showed no significant difference between Ww and Wh, which I believe was due to the loss of strength from the low hardness offsetting the increase in toughness that was gained by keeping the material so soft -- Wh was already very tough and equal to the best foreign armor steels. Also, trying to soften such metal to this extreme can be just as difficult as trying to harden it to its maximum, with just as unreliable results. Ballistically, I rate Ww as 1" (25.4 mm) Ww equals 0.95" (24.1 mm) Wh.

FACE-HARDENED ARMOR

In the BISMARCK, vertical or near-vertical armor designed to resist low-obliquity impacts by major-caliber projectiles was made up of "Krupp Cemented n/A" ("Case-Hardened and Decrementally-
Hardened Nickel-Chromium-Molybdenum Armor made by Krupp, New Type") (KC n/A). This form of armor is called 'face-hardened' in general. Chemically similar to Wh n/A and made in thicknesses from just under 4 inches (100 mm) to 14.96 inches (380 mm) - thicker plates were experimented with - this armor had its interior hardened in a manner that makes it much more hard and brittle on the forward surface facing the enemy (circa 650-700 Brinell, about as high as the Brinell scale can reach and equal to or higher than any other foreign face-hardened armors), while keeping it similar to Wh at the back of the plate (circa 240 Brinell, which is slightly higher than the average foreign armor of this type).

The first inch or so from the face surface of a KC n/A plate is carburized ("cemented") in a special oven to allow such a very high surface ("case") hardness and then the armor is heated in such a manner that the face layer of 41% of the plate's thickness is above a critical hardening temperature, but the remaining 59% stays below it (very careful control of temperature and time allows this). When all conditions of heat and time have been met, the plate is removed from the oven and quenched with high-pressure water until it is completely cold. The deeper the cooling occurs, the slower the heat is extracted and the slower the transition to the hard ("martensite") crystal structure, causing a gradual ("decremental") softening as one moved back from the face. Just behind the thin 650-700 Brinell cemented layer, the steel has hardened to 500 Brinell and this hardness gradually drops until the 240 Brinell level soft ("pearlite") crystal structure is reached at 41%.

The soft back soaked up shock transmitted through the face and kept the hard material from being punched out by fracture at its back like a b-b hole in a plate of glass; with such back support the hard face must be punched out from the front, which is much more difficult and results in attacking projectiles having their noses smashed to pieces by shatter, as well as suffering other forms of damage that either reduce penetration ability or prevent the projectile from exploding properly or both. The development and use of the AP cap on virtually all 20th Century anti-battleship armor-piercing projectiles was a direct effort to prevent such degrading projectile nose damage, with considerable success in some designs and less so in others.

Krupp developed the special nickel-chromium composition in 1894 (molybdenum was added only to KC n/A and a few foreign forms after WWI) to increase the metal's basic strength and to prevent the plate from cracking or forming inferior crystals when it cooled deep inside, which had prevented the deep decremental hardening process from being used with steel before this (only special super-thick high-carbon-content cast-iron domes for land forts made by the German firm of Gruson could be so hardened prior to this). By 1900, virtually all heavy side armor for all warships was made using variants of the original KC process-later called by Krupp "KC a/A" (KC Old Type) to distinguish it from its superior KC n/A successor. Foreign forms varied considerably in composition and hardening technique over the years from 1890 through 1945, with a few types, such as Japanese Vickers Hardened used on the WWII YAMATO Class warships, even eliminating the thin cemented layer to reduce the cost of manufacturing. These changes had various results on the armor's resistance to penetration -- some good, some not so good.

The original KC a/A armor had a softer, but more brittle, back layer than KC n/A due to inferior knowledge as to how to harden steel. Also, Krupp tried to harden the face to the maximum extent possible with much less attention to toughness. Other manufacturers, especially after WWI, found that adequate toughness to prevent the plate from breaking for as long as possible - which was difficult to achieve with such a hard and brittle face layer - was a great aid to improving the armor's strength and even Krupp (which was a very reactionary company) had to finally see the wisdom of this after WWI, which led it and most others to develop tempering (toughening) processes that greatly improved their face-hardened armors by the mid-1930's.

The original KC a/A had a thinner 33% face layer but this was less able to damage projectiles so Krupp increased the layer to 41% in KC n/A. Other manufacturers greatly changed this both ways, with some face-hardened plate types having very thin faces (U.S. 1921-23 Bethlehem "Thin Chill" Class 'A' armor with its 15% face, for example) or very thick faces (U.S. average post-1935 "Thick Chill" Class 'A' armor with its 55% face, for example). The thicker the face, the more effects scaling (making both the plate and projectile larger in step with one-another, but keeping the other properties the same) had on the plate and the weaker the resistance against larger projectiles, though a thicker face may cause more projectile damage and thus offset this in some cases. The change from 33% face to 41% face in Krupp KC armor had a small scaling penalty, but the generally higher steel quality more than made up for this.

British post-1935 "Cemented Armor" (CA) seems to have been the most resistant of all types when used in battleship thicknesses (10 inches (254 mm) and up). The British thinned down the face to only 30% of the plate and softened the cemented layer to only circa 600-Brinell, so that maximum plate toughness and reduced scaling effects worked together to increase resistance, and they did this without any noticeable loss in the armor's ability to break projectiles. Since only British battleships or battle-cruisers used face-hardened armor after WWI, thin face-hardened plates of this type were rare (4" (101.6mm) aircraft carrier deck armor was the only other major use).

On the other extreme, for cruiser-level armor 7 inches (179 mm) or less in thickness, the extreme face thickness of WWII U.S. Class 'A' armor caused the scaling effects to work in reverse to make that armor superior to its thinner-faced foreign contemporaries. U.S. cruisers thus had the best protection of any warships of their size. The thick face was an attempt to allow the armor to break the very superior U.S. armor-piercing projectiles that were developed at the same time. These projectiles were the best in the world at resisting damage, though they were sometimes slightly inferior in penetration ability if they and their foreign contemporary could both penetrate the same plate intact. Eventually the armor manufacturers had to give up trying to damage the best U.S. projectiles, but by then they had gone "over the top" in overall resistance and had made the thick-faced armor inferior to many foreign contemporaries in its thickest grades due to scaling, which had a major detrimental impact an WWII U.S. battleship armor resistance when not compensated for by other methods. The U.S. armor designers had some idea of this problem, as can be seen by certain modifications that they made, such as using Class 'B' homogeneous armor in the thickest plates on the faces of WWII battleship main gun turrets, something that was not done by any other navy, while retaining face-hardened armor on WWII U.S. cruiser turret faces up through 8 inches (203 mm) thick.

The rest of the BISMARCK was made up of a high-quality medium construction steel called "Schiffbaustahl III" ("Shipbuilding Steel Type 3"), similar to that used by foreign designs. These had a Brinell hardness of 120-150 and were much less tough than Wh or Ww since they were not designed to resist sudden projectile impacts. Interestingly enough, unlike most foreign ships, very little extra-tough, 160 Brinell-and-up "High-tensile" construction steel (HT or HTS or British/Japanese/Italian "D"-steel) was used in the BISMARCK, where medium steel was considered adequate unless a fully high-grade armor was needed, wherein Wh or Ww or Wsh was used instead.

ARMOR DISTRIBUTION

The armor protection of the BISMARCK was distributed in a more-or-less "conventional" manner with a few major exceptions that make these ships (and their contemporary German cruisers of the KM HIPPER Class and battle-cruisers of the KM SCHARNHORST Class) unique.

CONNING TOWERS

The forward conning tower-was heavily armored with 13.78" (350 mm) KC n/A sides and a 7.88-8.66" (200-220 mm) Wh roof. This is similar to most foreign designs, except for the British, who decided that such a heavy tower so high in the superstructure was stealing weight needed elsewhere (they were designing ships under the restrictions of the Washington Naval Treaty and needed every pound) and who replaced the heavy armor with more widely distributed 2.94-3.94" (75-180 mm) NCA in their new and rebuilt battleship bridge structures, making the bridge proof against fragmentation and nose-fuzed high explosive projectiles, but not direct hits by any cruiser or battleship armor-piercing weapon.

The use of heavy armor in a battleship's conning tower makes it absolutely proof against small- and medium-caliber guns up through heavy cruisers, barring a lucky hit right on a vision slit (some foreign designs even eliminated most of the vision slits by using periscopes poking through the roof). However, whether the armor is going to help against battleship-caliber guns is not certain. The impact shock of a projectile weighing roughly 0.75 to 1.5 tons and traveling in excess of a thousand miles an hour is unbelievable! The rather small enclosed conning towers were filled with relatively delicate equipment and even more delicate people. Unless the impact was very glancing and/or occurred at such a long range that the projectile could not penetrate anywhere near that thickness of armor, the shock of even a non-penetrating hit would be so great that the armored bridge would probably not be in working order afterwards for some time. If the armor were actually holed by the impact, the rapidly-moving punched-out pieces of such thick armor alone would be so dangerous that they would tear up the inside of the conning tower if the projectile itself was a dud or bounced off -- a 15" (38.1 cm projectile will punch roughly 850-980 pounds (385.5 - 408.2 kg) of armor out of a 14" (356 mm) face-hardened plate at right angles! In the case of the BISMARCK's conning tower, the British shells punched completely through it several times, anyway, making the matter rather hypothetical.

On the other hand, the unarmored upper-bridge-compass platform of the HMS PRINCE OF WALES was punched through by a projectile from the BISMARCK during its battle with that ship just after sinking the HMS HOOD, killing most of the ship's officers there. However, the projectile was not slowed by passing through the thin plating and immediately passed out of the far side without exploding (even if the fuze had been set off, an unlikely event an such thin metal, its circa 0.035 second delay designed for use in deep hull hits would allow the projectile to move 40-50 feet (12.2 - 15.2 m) under these impact conditions and thus to escape before exploding in most cases), so the Captain and another officer of the PRINCE OF WALES, who were both in this space, survived. This would probably not have been the case had the projectile penetrated through heavy armor and punched out high-velocity armor pieces weighing several hundred pounds in front of it, been slowed to a crawl that allowed its delay-action fuze time to explode the projectile inside the conning tower, and, even if a dud, been trapped inside the conning tower by the now-impenetrable armor on the far side so that it bounced around inside. Here, the ship's officers were not even in the lightly armored bridge space provided (they were standing on its roof) because many such officers felt that they could not see well enough through the narrow vision slits. It does not matter how much armor a conning tower has if the conning personnel are not in it!

Luck seems as much to do with the usefulness of heavy conning tower armor as any other factor.

BISMARCK's aft emergency conning tower only had 5.91" (158 mm) KC n/A armor, proof against fragments and light gun projectiles, again on a par with most non-British contemporaries.

DIRECTORS AND RANGE-FINDERS

The main armament, secondary, and anti-aircraft gun directors and range-finders were armored against fragments and light weapons only due to the impossibility of adding heavy armor so high in the ship's superstructure. The higher in the superstructure they were, the lighter the armor and the smaller or slower the fragments had to be to be stopped by the armor. This made some sense in that the higher in the superstructure the cupola was, the less nearby structure existed that could cause a projectile to explode and damage the cupola unless a direct hit on the cupola itself occurred. Those mounts were so small that the arguments against heavy armor in a conning tower were such more relevant here, meaning that even a glancing hit would incapacitate the director/range-finder until major repair work was done, so why bother trying to armor it against such hits? This agreed exactly with all foreign contemporaries.

Lack of adequate protection of directors and range-finders (later including radars) was an Achilles Heel of all such ships because loss of these extremely important fire-control devices virtually always would doom an isolated ship to destruction if the enemy still had use of their directors - the ability to hit the target is very poor when guns are under local control rather than director controls as was demonstrated time and again in both WWI and WWII. (Current-day missile weapons cannot even be fired in most cases if the fire-control system is not working properly, leaving zero capability.)

SECONDARY AND ANTI-AIRCRAFT MOUNTS

The BISMARCK had separate 5.91" (150 mm) twin-gun secondary turrets and 1.5" and 4.1" (37mm and 105 mm) anti-aircraft guns, with the 4.1" mounts being controlled by special stabilized, lightly-armored globe-shaped antiaircraft directors (two per side). The anti-aircraft guns had little protection except for thin flat gun shields, if that. The secondary mounts had their ammunition handling rooms under them protected by the 5.72" (145 mm) KC n/A upper side hull armor and 1.97" (50 mm) Wh armored weather deck and their turrets protected by 3.94" (100 mm) Wh faces and 1.57" (40 mm) Wh sides, rears, and tops. This was about average for such secondary mounts, though some contemporaries had twice the armor. Actually, the armor should have been 1.97" (50 mm) minimum for ensured protection against fragmentation from nearby major-caliber hits, since 1.57" Wh is piercable by the heaviest fragments - though admittedly very few of the total number of such fragments - of exploding battleship-caliber gun projectiles unless the impact is far away. Obviously a direct hit by any kind of cruiser or battleship armor piercing round (or even a high explosive round of significant size) would probably knock out a secondary turret.

The use of separate heavy secondary surface-target-only guns and light anti-aircraft-only guns (anti-surface use of the 4.1" guns was possible, but effective only against very lightly armored or unarmored targets and only at extremely close range) was typical of most warship designs at the beginning of WWII. The British and the U.S. both introduced medium-caliber dual-purpose guns -- 5.25" (133 mm) for the British and 5" (127 mm) for the U.S. -- for use against both lightly armored surface targets or, most important, aircraft in the late 1930's. Both nations had the great foresight to realize that any secondary gun that could not be pointed effectively at an aircraft had no place an a warship, as was proved conclusively during WWII. The U.S. Navy's highly-effective 5"/38 (127 mm) single and twin mounts were the most successful due to the superior fire-control systems that the U.S. Navy had and continually improved upon during that war.

MAIN ARMAMENT GUNS

The main armament mounts of the BISMARCK were arranged in the classic two-barrel super-firing turret pair forward and aft. The thickness of the KC n/A armor was 13.39" (340 mm) all around for the exposed portions of the circular barbettes, dropping to 8.66" (220 mm) KC n/A where it was behind the upper side hull armor and armored weather deck. The barbette armor ended completely at the main armored (third) deck which was 3.74" (95 mm) Wh over the magazines. (The BISMARCK's sister ship KM TIRPITZ had barbettes with a narrow exposed arc centered along the ship's centerline and facing toward the superstructure on either end that was only 8.66" thick because this armor could only be reached at a highly oblique angle unless the projectile tore through a large part of the superstructure first. This saved some weight which was used to increase the deck armor over the magazines to 3.94" (100 mm). This thickness of barbette armor was slightly thinner than most contemporaries and much thinner than U.S. battleships, which had barbettes that used 16-17.3" (406-434 mm) Class 'A' armor (the canceled USS MONTANA Class was to have used 21" (533 mm) Class 'A' barbettes!).

The rotating turrets are also slightly lighter in armor than the average foreign designs with 14.17" (360 mm) KC n/A near-vertical faces (port plates), 8.66" (220 mm) KC n/A vertical sides, and 12.6" (320 mm) KC n/A backs (this thicker back is due to it being used as a counterweight for the gun barrels to balance the turret). Most foreign designs used heavier faces except for the British HMS KING GEORGE V Class which used smaller 14" (356 mm) guns and only 12.75" (324 mm) CA faces (the lower scaling effects of thin-faced British CA partially offset this slightly low face thickness).

Except for U.S. battleships, all main-armament turrets of all post-WWI battleships used face-hardened vertical armor all around. However, all U.S. Navy's WWII-era battleship turrets had face-hardened armor sides and rears and barbettes, but used extremely heavy Class 'B' faces sloped back 30-40^o of 16-19.5" (406-495 mm) thick, made up of either a single thick plate or, for some ships, a 17" (432 mm) plate laminated over a 2-2.5" (50.8-63.5 mm) back plate.

Turret roofs on the BISMARCK were of the unique standard German WWI pattern, being "faceted," with a central flat rectangular 7" (180 mm) Wh region raised up above the upper edge of the turret sides and connected to the sides using prism-shaped 7" Wh sloped plates on the sides and front. This raised the roof of the turrets a couple of feet without having to increase the height of the heavy side and face armor and thus this design lowered the weight of the turrets. Most foreign contemporaries had turret roofs of that thickness or greater that were flat or slightly sloped to the sides or fore-to-back. However, the BISMARCK's steeply sloped roof edge plates were much less oblique than the flat central roof and were not increased in thickness to compensate. To me, that makes them weak spots in the turret; they should have been thickened to at least 9" (229 mm) or, if not, at least the front sloped plate should have been sloped at a much shallower angle, as it was the one most likely to be hit by the enemy that the turret was shooting at.

However, this weakness is not as great as that of French post-WWI battleships and battle-cruisers, which used face-hardened armor for all of their main armament turret roofs because they thought that steeply falling aircraft bombs were more of a threat to such areas than highly oblique-trajectory naval gun projectiles. A turret roof hit on the DUNKERQUE by the HMS HOOD on 3 July 1940 demonstrated the error of that by the huge, projectile-shaped hole made in the 5.91" (150 mm) turret roof that allowed the lower portion of the broken 15" (381 mm) projectile to pass into the turret behind the large mass of armor fragments, gutting that half of the divided turret and killing everyone there. This hit would probably have caused merely a long dent with perhaps a central slit split open at its bottom if the armor had been homogeneous (if so, the destroyed turret half might have still been put out of action, but probably nobody would have been killed and repairs would have been much more easily made).

Weak spots like these seem to act like magnets to enemy shells, as the many "fluke" hits in naval battles have shown again and again.

HULL ARMOR

The hull protection scheme of the German WWII armored warships was based strongly on their WWI designs and was significantly different from all contemporaries in several major ways.

BOW ARMOR

The bow of the BISMARCK was essentially unarmored except for very thin 0.787" (20 mm) Wh deck plating at the fourth deck level below the waterline extending about a third of the way toward the bow from the forward armored transverse bulkhead of the Citadel and light belt plating at the waterline to reduce the chance of fragments causing leaks. This level of protection of the bow was normal for ships of that period - some had no reinforcement at all of the bow area.

STEERING GEAR ARMOR

The stern was rather more heavily protected from the aft armored bulkhead of the central Citadel to the point where the rudder pinions projected out of the ship's bottom. After this point all armor abruptly ended. This armor consisted primarily of a "turtle-back" 4.33" (110mm) Wh deck at the waterline with a flat center that sloped down at the edges to slightly below the waterline at the side hull at an angle of circa 65-70 degrees from the vertical, covering the rudders, their machinery, and their control and power connections. The waterline hull was slightly reinforced much like the bow along the length of this deck. The end of this armored deck at the stem was capped by a narrow vertical transverse bulkhead 5.91 " (150mm) thick of KC n/A to slightly below the waterline. [NOTE: Some sources give this bulkhead as Wh or even Ww, but my data from Krupp's own specification documents limits Ww to a maximum thickness of 1.97" (50mm)] A 1.77" (45mm) vertical transverse bulkhead of Wh continues the 5.91" bulkhead to the ship's bottom and another continues it upward to one full deck above the waterline.

This protection of the rudders from shell hits was virtually identical to most contemporaries and seems to have been adequate. It used the concept of keeping the target as small and as low down as possible and was designed primarily against flat-trajectory hits from the side; steeply failing projectiles at long range or aircraft bombs would have only the single 4.33" armored deck to stop them unless they were set off on the thin, unarmored weather deck, second deck, or third deck beneath it and exploded before reaching the armored deck about 48" (122 cm) below the third deck level. Such thin plates were unlikely to set off the fuze of a steeply falling armor-piercing bomb or projectile of any size, however.

I will assume that the projectile or bomb is not set off by any of the thin upper decks and that each unarmored deck was equal to 0.5" (12.7 mm) of Wh (a rather generous value since they are only made of Schiffbaustahl III, not armor, but internal bracing and other bits and pieces of metal will usually also get in the way of the bomb or projectile and this takes them roughly into account, too). The first deck would strip off the windscreen of any projectile (8.6-5.3% of the total projectile weight, with the larger the projectile, the more the windscreen weight tended toward the low end of this range), but not the AP cap of any projectile over 6" (152mm), but this loss has very little effect on penetration, so I am ignoring it. The total steering deck armor protection can be computed as follows:

(1) The thin upper decks are not likely to noticeably deflect the projectile or bomb so it will travel in a straight line through all of the decks that matter (the 4.33" lowest deck may deflect the projectile after it penetrates, but this means very little as the bomb will be through all of the protection at that point, anyway). A simple sum of the kinetic energies needed to pierce each plate separately will therefore give the total kinetic energy needed to pierce them all, which can be turned back into a minimum plate thickness.

(2) The De Marre Nickel-Steel Armor Penetration Formula gives reasonable "ballpark" values for estimating homogeneous armor penetration over most of the range of thicknesses of interest (it does not work with very thick plates, but this is not our problem here). This formula is

T = (K)V^1.42857

where T is the plate thickness barely penetrated at striking velocity V and K is a constant for a given plate type and projectile design and obliquity of impact.

(3) The formula for kinetic energy is

KE = (0.5)(W/g)V²

where W is the projectile's weight, g is the acceleration of gravity and V is the projectile's velocity. (Note that if W is measured in metric grams or kilograms, it already has been divided by g so that the division is only needed for English pounds.)

(4) Combining the equations in 2 and 3, above the total kinetic energy needed to penetrate the entire plate array is

KE_(total) = KE_{(plate 1)} + KE_{(plate 2)} + ... + KE_{(last plate)}

and it can be transformed to

T_total = (T₁^1.4 + T₂^1.4 + ... + T_last^1.4)^0.7142857

All of the K, W, and g terms canceled out and were eliminated.

(5) Using 0.5" for plates 1, 2, and 3 and using 4.33" for plate 4 (the last plate), the value of T_total is 4.77" (121 mm).

This steering 'plunging fire" protection is lighter than the armor protection afforded amidships, but it is very similar to the steering protection afforded by most contemporary warships (the Italian VITTORIO VENETO Class and British HMS KING GEORGE V Class were virtually identical in this protection to the BISMARCK). Against flat trajectory fire at close range, the shallow (22^o from the horizontal if sloped as the amidships plates of the same thickness were) slope of the 4.33" edge plates or the horizontal 4.33" centerline plates should cause many projectiles to glance off. However, it must be realized that the protection is not the same as the main amidships side/deck protection and rudder damage can occur at ranges where the amidships region would not suffer major damage, though the single thick 4.33" plate used here may offer more protection under some conditions than the divided armor scheme used amidships.

Also, diving shells that hit below the waterline could easily get under the very shallow protection in this region of the ship, where the hull does not extend as far down into the water to give the propellers and rudders room to function. Such diving shells were obviously not considered a major threat by the German designers but a great many hits in WWII were underwater hits; this will be discussed in more detail below.

AMIDSHIPS ARMOR PROTECTION OF THE "CITADEL"

While the armor protection scheme of the BISMARCK is similar to its contemporaries in most respects, as indicated above, the amidships hull armor scheme protecting the ship's "vitals" - magazines, boilers, engine rooms, electrical generator rooms, power and communication switchboards, gun plot rooms (for range-keeping electro-mechanical computers and stable elements/gyroscopes), and so forth - was definitely unique to German warships in WWII. This portion of an armored warship is generally termed the "Citadel" because it represents the 'core' of the armored "castle" in the hull. This armor scheme was a "beefed-up" version of the scheme used before and during WWI by German and many foreign battleships, which was abandoned by every other nation except Germany immediately after the last ships designed before or during that war were finished (note the enormous change between the HMS HOOD, which was the last WWI-type battleship/battle-cruiser built by Britain, and the HMS NELSON and HMS RODNEY, which were designed just after that war as HOOD-sized "modern" battleships, but later reduced in size and speed because of the restrictions of the Washington Naval Treaty of 1922). Germany seems to have been the most reactionary of all nations in its large warship designs, which is strange after it had built the very radical and advanced "Pocket Battleships" of the DEUTSCHLAND (later LUTZOW) Class in the late 1920's and early 1930's.

The BISMARCK's Citadel armor was as follows:

HORIZONTAL-ONLY (DECK) PROTECTION

The amidships deck armor consisted of a 1.97" (50 mm) Wh weather deck, then a roughly 0.5" (12.7 mm) Wh-equivalent Schiffbaustahl III second deck (including everything that might got in the way of a falling bomb or plunging projectile), and finally the main armored third deck just above the waterline, which was 3.15" (80 mm) Wh over the amidships region and 3.74" (95 mm) Wh over the magazines surrounding the main gun turret groups fore and aft (its sister ship the TIRPITZ had 3.94" (100 mm) Wh over the magazines). The decks were spaced about 8.5' (2.6 m) apart. About 30% of the third deck area measured inward 17.4' (5.3 m) from both side hulls was abruptly sloped downward at 22^o from the horizontal (68^o from the vertical) so that its outer edges met the main side belt armor just above the belt's lower edge, below the waterline, making a 'turtle-back' deck similar to that over the steering gear and, on the sloped portion, with the same thickness of 4.33" (110 mm) Wh. A light horizontal deck of probably only about 0.3" (7.62 mm) Wh-equivalent covered this sloped region as an extension of the flat part of the main armored third deck to the ship's side, allowing this space to be used for supporting equipment and for passageways. Below the sloped armor was the ship's fuel oil, distilled boiler feed-water, and the anti-torpedo liquid/void/bulkhead system that extended all of the way down to the ship's bottom hull. The 1.77" (45 mm) Ww vertical main anti-torpedo bulkhead separating the main hull compartments from the outboard anti-torpedo and liquid storage systems was located exactly under the "knuckle" where the sloped edge and central flat portions of the main armored deck met.

Using the same technique used to estimate the steering gear total protection, the value of T_total over the amidships region on the central flat deck would be determined by a plate 1 of 1.97", a plate 2 of 0.5", and a plate 3 of 3.15", which results in T_total equaling 4.4" (112 mm) plus whatever the bomb or projectile had to pass through in the superstructure to reach the hull, which might add as much as another inch (25 mm) or so to the total in some cases or nothing at all in other cases. This is slightly on the light side compared to the BISMARCK's foreign contemporaries, all of whom had total effective deck thicknesses of at least 5" (127 mm) and usually much more. The two-deck space between armored decks in the BISMARCK was larger than most, which may compensate in some cases, but this depended on the enemy's projectile or bomb fuzing delays, not on the strength of its own armor; WWII fuze delays were longer and more reliable than in WWI.

Similarly, over the magazines, plate number 3 becomes 3.74" and T_total becomes 4.92" (125 mm). Here the only large things above the weather deck are the main armament turrets, which cover much of the area and which therefore have a good chance of being hit instead of the three-deck hull around them if steeply plunging bombs or projectiles hit the magazine regions. Again, this deck armor is lighter than most contemporaries, who added another 0.5-1" inch (13-25 mm) at least over their magazines compared to their amidships spaces, making their decks over the magazine at least 5.9" (150 mm) in total effective resistance.

The effective amidships deck armor values computed above seems to straddle the 4.77" value given for the steering gear. However, there is a significant differences caused by the 1.97" Wh weather decks:

(1) It can break up large-cavity, weak-bodied general-purpose bombs, greatly reducing their explosive effectiveness even if they do penetrate through it.

(2) It is proof against most fragments and blast effects except for those from large projectiles or bombs that detonate "high order" while in physical contact with it; even a gap of a few feet will prevent almost all standard projectile and bomb fragments from penetrating and make most blast effects above the deck merely a loud noise below it.

(3) It can deflect even large-caliber projectiles hitting at a shallow angle during a relatively close-range engagement.

(4) It is proof against virtually all light-caliber guns through 5.5" (140 mm) or so - at the short ranges where these can get a significant number of hits, the trajectories are flat enough to prevent penetration even if these light guns were firing "piercing" projectiles and not the more likely nose-fuzed HE projectiles with no armor penetration ability to speak of.

(5) It will tear off the AP cap of any impacting projectile, reducing the projectile's weight and, at high obliquity, reducing penetration ability against any later plates due to the more pointed nose of the cap-less body. At extreme ranges where the angle of fall is such that the impact obliquity an the 1.97" Wh weather deck is below 50^o, the loss of the cap improves penetration, but such hits will be rare due to the small chance of hitting (even if the guns can elevate enough to allow this in the first place). The change in the projectile weight and nose shape by stripping off the AP cap render the simple spaced-plate addition formula used above rather inaccurate, even if the projectile is not deflected by the weather deck.

(6) It can be guaranteed to set off the fuze of any projectile or bomb that is not an out-and-out dud and to slow down the penetrating projectile or bomb somewhat due to the energy needed to punch through it. As a result, except for long-delay fuzes such as those used on the Japanese Type 88 and Type 91 "diving" armor-piercing projectiles or on some aircraft bombs, there is a good chance that the projectile or bomb's own fuze will destroy it in the two-deck-deep 17' (5.2 m) gap between the weather deck and the main armor deck, causing major damage in this region, but preventing damage in the much more important spaces below the main armor deck (the main armor deck is proof against virtually everything that cannot directly punch through it by sheer momentum alone). This use of space to enhance protection is especially likely in a short-to-medium range battle where gun projectiles are coming in at shallow angles where they would move a very long horizontal distance while moving downward the two-deck vertical distance after a weather deck hit. For example, even with a projectile falling at a 30^o angle of fall at rather long range (this angle of fall is given by a gun elevation near 20^o, which is at the upper edge of what the German designers felt were the likely battle ranges in the stormy North Sea or North Atlantic), to fall the circa 17' (5.2 m) distance between the armored decks would mean traveling a total of 34' (10.4 m) slantwise, which is near the maximum for the typical WWII American or European 0.025-0.035-second delay-action fuze in an armor-piercing projectile hitting at such a range. At shorter ranges, the slant distance increases rapidly with shallower trajectories, offsetting the higher striking velocities and, thus, longer fuze-limited travel of the projectiles before detonating. Aircraft bombs hit at much lower velocities and the deceleration of penetrating the 1.97" weather deck would make the time of travel in the two-deck gap even longer, compensating considerably for the much steeper trajectories of such bombs and the resultant shorter slant distances traveled between the armored decks. Note that it is extremely important that nothing of a critical nature to the ship during a battle be located in this sacrificial upper hull region. If any critical pipes or cables must pass through this region, they should be heavily armored. Some of the damage inflicted on the BISMARCK near the beginning of its last battle may have been caused by a failure to follow this rule.

(7) This weather deck armor uses weight that could have been used to "beef up" the main armor deck. After adding a 0.25" (6.4 mm) value to the entire deck to take into account the spreading out of the thicker slope armor across the entire new flat deck, the same total weight of deck armor would have made single solid 5.37" (136 mm) amidships or 5.96" (151 mm) magazine Wh deck at the second deck level an the upper edge of the main armored belt, almost exactly what most American and foreign European battleship contemporaries had, which is considerably more resistant to penetration, though it would sacrifice the uppermost hull region between the weather deck and the new armored second deck (this hull region is of little value for floatation purposes and more than made up by the extra protected room under the new armored deck that would allow more space for important machinery, larger boilers, and so forth) and, more important, would reduce or even eliminate the space between the decks that allowed projectiles to detonate prior to hitting the armored deck. This latter would greatly reduce the deck protection against projectiles or bombs that could penetrate either deck scheme if no premature fuze action occurred, which would mean a careful analysis of the typical enemy weapons to see if this was likely under most battle scenarios. A compromise to increase the weather deck armor thickness slightly to improve its chances of setting off fuzes, such as American battleships with 1.5" (38mm) STS weather decks did, is possible, if considered worth the results. A single-armored-deck scheme would also eliminate the sloped portions of the deck that reinforced the main belt armor, which would be a very significant loss in side protection, as we will see, but the advent of radar-controlled long-range gunfire and much more effective aircraft dive bombers during WWII made deck armor much more important and this meant that the use of the low, sloped deck to protect the ship's sides was therefore much less important.

(8) As will be seen in the analysis of the BISMARCK's deck protection below, the 1.97" deck has the unfortunate property that it will deflect a completely penetrating projectile at high obliquity downward, decreasing the impact obliquity against the lower armor deck and reducing the protection afforded by the lower deck at a range of striking velocities and impact obliquities that the ship would otherwise be protected against. If the weather deck were reduced in thickness to only 1.5" (38 mm), which is common in its contemporaries, it would not do this to battleship-caliber projectiles and it would be more effective! This is one of the few cases where increasing the armor decreased the protection it afforded! This will be analyzed in detail below.

UPPER HULL ARMOR

The gap between the top edge of the main armor belt, which ended at the second deck level, and the armored weather deck one deck higher was filled in the BISMARCK by a 5.71" (145mm) KC n/A vertical plate set over about 2" (50.8 mm) of teak and about 0.5" (12.7 mm) of Schiffbaustahl III hull plating. My face-hardened armor lamination formula cuts the backing plate thickness in half after multiplying it by a 0.8 quality factor for post-WWI medium steel, giving 0.2" (5.08 mm), multiplies the wood thickness by 0.01, giving 0.02" (0.51 mm), and then simply adds them to the face-hardened armor thickness to get 5.93" (151 mm) KC n/A equivalent. This is the side armor of a well protected WWII heavy cruiser, which agrees rather well with the 1.97" Wh weather deck, which is also typical of the heavier designs of WWII cruiser deck armor.

The transverse bulkheads at the ends of the upper Citadel were of 3.97" (100 mm) to 5.71" KC n/A, with the thicker plates near the centerline. I would have reversed this and had the thicker plates outboard where there is less hull and bulkhead and deck plates to pass through to get to the armored bulkhead. This makes the upper hull armor more-or-less of equal protection from all sides.

This armor is proof against all fragments and all nose-fuzed high explosive projectiles, even if they make a direct hit in most cases. At longer ranges it was proof against most cruiser guns, especially those firing large-cavity base-fuzed Common or Semi-Armor-Piercing (SAP) projectiles without armor-piercing caps, as did a great many cruiser guns at the time. Note that the British used such an uncapped Common projectile (CPBC) in their 6" (152 mm) cruiser guns, but they also used an unusual compromise 8" (203 mm) projectile that was an SAP design with an armor-piercing cap added (SAPC), which gave a rather good capability against medium-thickness face-hardened armor such as the BISMARCK's upper side hull at near right-angle impact, though it broke up against heavier armor or at high obliquity. The U.S. Navy used uncapped Common projectiles for both size guns during the 1920's and 1930's but in 1937 they decided to use face-hardened Class 'A' armor on their new cruisers and therefore switched over to fully effective, capped armor-piercing projectiles during WWII for all guns over 5" (127 mm), except for old 6" guns converted to submarine deck guns, which retained the older Common projectile ammunition as more effective against the targets that they would be firing against.

However, this upper side hull offered no protection whatsoever against battleship caliber guns at any range or against cruiser guns at close range, though it did insure that the projectile fuzes would be set off and the projectile slowed down appreciably, with much the same result as hits on the armored weather deck. For those weapons that could pierce the main armor deck even after going through the weather deck or upper side armor, the time delay between the first armor impact and the main armor deck impact would contribute to the protection of the vitals by causing a higher percentage of projectiles and bombs to explode in the upper hull region, as previously explained under the horizontal armor discussion. However, the weight used up in this upper hull armor could have added at least an inch (25.4 mm) to the main armored deck or at least 2.5" (63.5 mm) to the main side belt - the deck increase would have been more useful, in my opinion, allowing a second deck-level armor deck approaching a near-YAMATO-scale 7" (179 mm thickness). Alternatively, a compromise 5.91" (150 mm) amidships and 6.3" (160 mm) magazines Wh armored deck and a 14.17" (368 mm) KC n/A main belt are possible on this displacement if the upper side armor were eliminated and the two armored decks combined into one solid deck at the second deck level. Whether this increase would make much difference in most naval battles would have to be carefully worked out. Considering what happened to the BISMARCK in real life, it is entirely possible that even increasing all of the ship's armor by 50% would not have made a single ounce of difference to the final outcome of its last battle!

The only justification for this upper belt design would be in a general fleet action where small enemy ships might get close enough to get a significant number of hits on the upper hull. However, with the German Navy so small and isolated to the point where ships were sent out more-or-less on their own, the only important ship adversaries were going to be enemy battleships and the last voyage of the BISMARCK would be the rule, not the exception. This made it absolutely important to maximize the deck armor protection against aircraft bombs and maximize the hull design against aircraft and submarine torpedoes to prevent them from crippling the ship so that it could be ganged up on by surface forces, even at the expense of some side protection - few hits on the main side belt armor of battleships happen in most cases unless the ship is already helpless and can be fired on point-blank, at which point the side armor is of little consequence! The upper side hull armor and heavy weather deck armor were luxuries that subtracted from more important portions of the ship needed for go-it-alone voyages.

DECK ARMOR COMPARISONS

The BISMARCK's own 38 cm S.K. C/34 (14.96" Major Caliber Naval Cannon Developed in 1934) fires a 1764 lb (800 kg) 38 cm Psgr. m. K. L/4,4 projectile (14.96" Armor-Piercing Projectile with Armor-Piercing Cap and a Total Length of 4.4 Projectile Diameters) at a muzzle velocity of 2690 feet/second (820 m/sec). Range and homogeneous armor penetration tables used here for this gun are from G.Kdos. 100 ("Secret Command Document #100"), the 1940 German Navy's "Gunnery Bible," a copy of which was discovered by the U.S. Navy just after WWII. My U.S. Navy test data does not completely agree with this document's penetration curves, but they both give "intertwined" results when plotted on the same graph. Therefore, I am using the German curves until I am sure that I have better data of my own.

All comparisons will be with this gun, assuming a complete penetration of the armor. Rather little armor material is thrown from a homogeneous armor plate, even if complete penetration occurs, so that barring a detonation of the projectile while still touching the plate at anything less than a complete penetration will have little effect an a large warship hull.

Under those conditions where the AP cap is stripped off by hitting steel plating greater than 1.2" (36 mm) (0.08 times the 38 cm projectile's diameter) at any obliquity, I will substitute for further penetrations my U.S. Navy homogeneous Class 'B' armor penetration tables for a pointed projectile with a nose shape similar to (but slightly more pointed than) the nose shape of the uncapped 38 cm projectile, which had a reduced weight of 1506 pounds (683 kg). A plate of 1.2" or more of any steel will strip off this projectile's AP cap at any impact angle, according to my U.S. Navy and Army test data for projectiles larger than 1.46" (37mm) in diameter.

A projectile that barely penetrates will be moving roughly at right angles to the plate when it exits the plate's back at low velocity (note that at over 45^o obliquity against thin armor, the projectile may be moving sideways or even base-first when it does so!).

Also, to a good first approximation, if the projectile passes through a plate at over the velocity needed to punch through twice the plate's thickness at the given impact obliquity, I assume that the projectile is essentially not deflected at all in its direction of motion and remains going nose-first at high velocity. For striking velocities in between, I use the following crude formula for the exit angle (EX) of the projectile measured from the normal (right-angle line) to the plate's back (and face for a constant-thickness plate) which will define the impact angle on the next plate in line when its position and inclination are known

EX = (0.5)(Obliquity Angle){1 - COS[180((V_s /NL)^1.42857 - 1)]}

where Vs is the striking velocity and NL is the U.S. (and German) "Navy" Ballistic Limit (the velocity which will allow the projectile to barely completely penetrate the plate at the given obliquity angle). If (V_s/NL)^1.42857 is greater than 2, simply assume that EX equals the obliquity angle (no deflection) and do not bother with the rest of the EX formula. The given formula's 1.42857 exponent is based an the De Marre Nickel-Steel Penetration Formula, which gives a good approximation of homogeneous armor penetration over the middle thickness range (0.25-1.0 times the projectile's diameter) when adjusted for the higher quality steel used in WWII. Also, the formula assumes that projectile damage is a constant over the NL to V_s interval, which may not be strictly true for real impacts.

The remaining velocity V_r after penetrating a homogeneous armor plate is given crudely by the conservation of energy formula

V_r = (V_s² - NL²)^0.5

where I assume that no significant amount of armor is thrown from the plate, and that the projectile's weight does not change, so that the energy absorbed by the plate is roughly constant for all values of V_s above NL. (This is not really correct, but the error is relatively small compared to the other sources of error.) For face-hardened armor, my formulae are more complex due to the large armor plugs thrown during penetration. At velocities just above the NL, where deflection is greatest (E_x is close to zero), the value of V_r is somewhat less than given by the above formula due to the additional energy lost in deflection effects as opposed to pure penetration, but the error rapidly decreases as deflection becomes less and less as striking velocity goes up. However, large deflections also cause the projectile to wobble considerably and to suffer more damage, so the penetration ability of the projectile is degraded in more complex ways when V_r is small compared to V_s, making the error of this formula rather irrelevant. I make the rule-of-thumb assumption that deflections (Obliquity Angle minus Exit Angle) over 45^o result in projectiles that are probably not moving nose-first in a predictable manner, but that lesser deflections can be considered stable nose-first penetrations for our purposes.

In this amidships deck armor comparison, I am assuming impacts go through the upper side hull or weather deck above the edge of the main armored belt (the main belt will be covered separately below) before hitting the lower (main) armored deck. Also, note that the sloped portion of the BISMARCK's main armored deck on the far side is sloping away from the firing gun by an additional 22^o added to any impact obliquity and can safely be assumed to be invulnerable due to this (also, any penetrating hits that did occur in this space would end up in the far side's anti-torpedo system where the deep liquid layer backed up by the 1.77" Ww inner holding bulkhead would stop all fragments and smother any blast from an exploding projectile). This deletes 17.4' (5.3 m) from the ship's vulnerable deck width.

The near side sloped lower deck area was almost completely shielded by the main side belt for most possible impacts and the lowest angle of fall that could hit even its upper edge at the joint with the flat portion of the deck after penetrating the bottom edge of the upper side hull armor is 26^o due to the 8.5' (2.6 m) vertical gap between the lower deck and the bottom edge of the upper side hull. Since the upper side hull armor is too thin to deflect the 38 cm projectile at a Target Angle of 90^o (i.e., broadside-on target), this 26^o is the true angle of fall that gives a range of 29,000 yards (26,500 m) and a striking velocity of 1526 feet/second (465 m/sec). Below this range, the near side sloped deck area can be deleted from the vulnerable deck area, too, resulting in a completely invulnerable main armor deck, barring a fluke hit of some sort.

I am assuming that 80^o is the highest obliquity where complete penetration is possible no matter how thin or weak the steel deck is. I have almost no data above this very high obliquity, but what data I do have points to even unarmored mild steel decks deflecting heavy battleship-caliber shells. This fixes the minimum angle of fall for deck armor evaluations at about 10^o for a target ship that is not rolling. If rolling is taken into account, it is possible for some deck structures to be pierced if hit just the wrong way at the wrong time, but this is a topic based on luck, not careful analysis - the ship designers must realize this and either try to throw in a little added compensation (how much is enough?) or ignore it.

The base fuze of the German 38 cm armor-piercing projectiles had a fixed 0.035-second black-powder delay base fuze designated the "Bd.Z. C/38" (Base Fuze ("Bodenzunder") for 38 cm armor-piercing projectiles). This fuze was much improved over its WWI, 0.025-second-delay predecessor, but still had poor reliability from reports from WWII battles. Many such fuzes would be reliably set off at right-angles impact by either a hit on a single steel plate (any kind of steel) of over 0.07 times the projectile diameter (0.07 'caliber') in thickness - 1.05" (27 mm) for the German 38 cm projectile - or by hitting two steel plates spaced a few feet apart each of which was at least 0.05 caliber thick - 0.75" (19 mm) for the 38 cm projectile. Certain highly 'safed' base fuze designs (improved safety during handling and storage prior to firing, not especially for better function at the target, though the latter also was incorporated in some of these designs) introduced during the late 1930's and during WWII by the U.S. and British navies, such as the widely-used U.S. Mark l8, 19, 20, and 21 base fuzes, eliminated the multiple plate sensitivity, requiring a minimum 0.07 caliber plate at right angles. At oblique impact, some designs allowed a thinner plate, but other primitive or poorly-designed fuzes would fail to function at all at any significant obliquity (only after WWI was oblique impact made a major projectile or fuze criterion). U.S. WWII base fuzes would be reliably set off by roughly 0.0625 caliber-thickness steel plates at 20^o obliquity (16" (406 mm) projectile tests) and 0.03125-caliber-thickness steel plates at 80^o obliquity (5" (127 mm) projectile tests), giving the following crude formula for the minimum plate thickness in calibers to set off a base fuze, which I will call T_fuze:

T_fuze = (X){(0.5)[1 + COS(2(OB))] + (0.4537)SIN^5.7019 (OB)}

where OB is the Obliquity Angle (zero is right angles to the plate) and "X" is 0.07 for a single plate or, for those fuzes set off by two plates hit in rapid succession, 0.05 for each of the two plates. The maximum obliquity value OB to use in this formula is 61^o, which reaches the minimum single-plate value of 0.03125 caliber, which is the "floor" value for that case; above 61^o obliquity use the 0.03125 caliber minimum for the single plate case - 0.47" (12 mm) for the 38 cm projectile - or a 0.0223 caliber minimum for the two-plate case - 0.33" (8 mm) for the 38 cm projectile. Note that these values are for an undamaged fuze and do not care whether or not penetration was achieved. Also, above 80^o obliquity fuze function is very chancy - many fuzes, including the German 38 cm design, attempted to include a "graze" feature for high obliquity impacts, but I do not know how effective most of these were. I am not sure as to the operational boundaries of the German fuze, but looking at a cross-section of it leads me to assume that it follows the above formula and retains the two-plate function due to its rather simple internal configuration (the Japanese used base-fuzes of very similar design); it was not of the "absolute" safety, intricate WWII U.S. type like the Mark 21.

The penetration ranges give the minimum range that the deck can be pierced. If there is a maximum at a longer range in some armor configuration, it will also be given, though this is rare. Note that the probability of penetrating the upper side hull rather than the weather deck prior to hitting the main armored deck goes down very rapidly with range simply because ships are so much wider than the height of the upper side and the projectile's angle of fall increases rapidly with range. Note also that in some cases there will be a minimum range for penetrating lower deck hits that go through the weather deck first simply because the penetrating projectile will hit the far side of the ship instead of the main armored deck if deflection remains low enough, even assuming a hit at the very edge of the near side of the weather deck. Below this range, only upper side hull hits can reach the main armor deck.

The geometry of the BISMARCK's decks amidships at right-angles to the keel (Target Angle of 90^o) gives a horizontal distance of 100.5' (38.6 m) from the near side to the far side's armor deck flat/slope joint. With the vertical distance between the weather deck and the main armor deck being 17' (5.2 m), the shallowest angle of fall is 10^o for a projectile that is undeflected by a hit on the near edge of the weather deck and still hits the very far edge of the flat portion of the armored deck (if it penetrated there it would immediately hit the 1.77" (45 mm) Ww far side torpedo bulkhead from the back and only cause major damage inside the ship if it failed to penetrate that bulkhead and blew up on its inside face). If the projectile comes in from a more oblique Target Angle(target ship moving toward or away from firing ship), the allowed distance would be greater, though there is then more chance of hitting many thin transverse or longitudinal vertical bulkheads at a high obliquity which would reduce the penetration ability of the projectile as it moved downward toward the main armored deck. Around the main armament turrets, the barbettes would be impacted much of the time before the projectile moved very far inboard.

If the projectile penetrates the weather deck with a much reduced remaining velocity (V_r is not zero, but is much less than V_ss), then the value of EX would be less than the impact obliquity (which equals 90^o minus the angle of fall on a flat deck) and this results in a steeper impact angle on the lower main armored deck (here also EX). Such a situation might compensate for the reduced striking velocity (here V_r) on that deck if the lower armored deck is thin enough. This interplay between V_r and EX complicates the analysis considerably! This is especially true with the BISMARCK, as we shall see!

In the case of the BISMARCK's amidships deck armor, at an angle of fall of 10^o the range for the 38cm gun is 15,600 yards (14,300 m) and the striking velocity is 1896 feet/second (578 m/sec). Using the G.Kdos. 100 penetration tables and extrapolating the plotted curves by eye from the maximum given obliquity of 70^o (given as 20^o in the tables because the German Navy measured right-angles as 90^o, not 0^o as the U.S. Navy and I do), the 1.97" Wh weather deck needs only 1312 feet/second (400 m/sec) to be completely penetrated at 80^o obliquity. Thus the weather deck can be pierced at the minimum possible range. With this NL, for the 15,600 yard range, my formulae above give EX equal to 62.7^o and V_r equal to 1396 feet/second (417 m/sec). Using my uncapped projectile penetration formula with OB=EX and V_s = V_r, the 14.96" projectile can pierce the 0.5" intermediate and the 3.15" armored deck. (However, if the value of EX is increased to just 64^o, lower armored deck penetration ceases to occur.) Thus, if my formulae are even approximately correct, the entire amidships non-magazine deck armor structure of the BISMARCK is ineffective against its own gun at the closest range that penetration of the weather deck is possible! At this range, hits are more likely, too! This is not good news for that ship!

In addition, the German projectile has a nominal delay of 0.035 second. At 1369 feet/second, this gives 47.9' (14.6 m) and at 62.7^o the 17' inter-deck gap becomes a slant 37.1' (11.3 m), well within most fuze delay variation (most delay errors cause the delay to be too long, not too short). EX must be increased to just 69.3^o, before the slant distance increases to 48.1' (14.7 m), where all delays that are on time or short are now incapable of reaching the lower armored deck. Thus, while the large two-deck gap between the decks does have some use against projectiles with short or erratic fuze delays, this was more effective in the original WWI designs upon which the BISMARCK was based because WWI projectile fuze delays were much shorter, if present at all, and base fuze designs were quite primitive and unreliable by WWII standards.

How big is this close-range zone of 3.15" deck vulnerability caused by the 1.97" weather deck deflecting the projectile? Obviously, when all deflection ends due to a decrease in the weather deck NL as the angle of fall increases (this angle increases faster than the striking velocity goes down), the close-range deck vulnerability will be gone. However, it should disappear more rapidly than that, since the deflection need not go completely to zero to stop having its effects. Also, it must kept firmly in mind that these numbers are due to my formulae, which are just best-fit approximations to my existing data. They may not give absolutely correct results, but rather a good indication of what kind of results are to be expected. The major point here is that without a thorough analysis of a problem, unexpected results (usually of a counter-productive type) can compromise any solution - "Murphy's Law" is true!

My computations indicate that the 3.15" deck's zone of close-range vulnerability is not very wide. When the range increases to 16,000 yards (14,600 m), with an angle of fall of 10.3^o and a striking velocity of 1884 feet/second (574 m/sec), the 1.97" plate's NL becomes 1292 feet/second (394 m/sec), which gives an EX of 64.7^o and a V_r of 1371 feet/second (417 m/sec). My formula for an uncapped projectile of 14.96" diameter and 1506 pounds body weight of the now-uncapped 38cm AP projectile gives an NL for the 3.15" plate at 64.7^o obliquity of 1373 feet/second (418 m/sec), which means that the close-range zone of 3.15" deck vulnerability ends; it was only 400 yards (366 m) wide. Note that if the weather deck were made thicker, deflection would increase and this vulnerability zone would get wider, not narrower, for some range of thicknesses before finally being reversed only when the value of V_r dropped too low to penetrate the lower main armor deck even at normal! Using a smaller gun has the same effect!

While seemingly insignificant, the fact that this "island of vulnerability" can exist at all means that the very simplistic assumptions many are tempted to make concerning ship design (or anything else, for that matter) may hide fatal flaws. Sometimes there is nothing that can be done to eliminate such defects, but they should not come as a completely unexpected surprise!

The 3.74" (95 mm) lower armored deck over the magazines does not have this close-range vulnerability to the 38 cm projectile, but it doesn't miss it by much. It takes 1492 feet/second (455 m/sec) to pierce the entire magazine armor protection at 62.7^o obliquity. According to my formulae, if the weather deck's exit angle and the impact obliquity on the lower plate was 60.6^o instead of 62.7^o the magazine would be penetrated, too. Not much room for error!

Beyond the close-range zone of deck vulnerability caused by the 1.97" weather deck, the 3.15" (80 mm) amidships main armor deck remains invulnerable until a range of 28,100 yards (25,700 m), where the angle of fall is 24.6^o and the striking velocity is 1540 feet/second (469 m/second). There is of course no deflection of the projectile and the NL of the weather deck is 633 feet/second (193 m/sec), giving a V_r of 1403 feet/second (428 m/sec), which is the NL for the 3.15" portion of the main armor deck at 65.2^o obliquity (=90^o - Angle of Fall) without an AP cap. This is still a noticeably shorter range than any main armor deck of any of its contemporaries, indicating a long-range weakness in this ship, even if the close-range deck problem is ignored.

The 3.74" (95 mm) main armor deck over the magazines remains invulnerable from hits through the weather deck until a range of 30,700 yards (28,100 m) is reached, where the angle of fall is 28.7^o (a 61.3^o impact obliquity against a deck) and the striking velocity is 1506 feet/second (459 m/sec). The NL of the weather deck is 538 feet/second (164 m/sec) at 61.3^o obliquity and the V_r after penetrating the weather deck, which is the NL of the 3.74" deck at 61.3^o obliquity, is 1407 feet/second (429 m/sec). This is still below the typical foreign contemporary, but not by very much.

What about the hits on the 5.93" (151 mm) KC n/A effective thickness of upper belt prior to hitting the lower main armor deck from a Target Angle of 90^o? Such hits are more likely at closer ranges than penetrating weather deck hits, with the vertical distance between the lower main armored deck and the bottom edge of the upper belt being 8.5' (2.6 m), and the distance to the top edge where it supports the edge of the weather deck being 17'.

My data indicates that the thin vertical upper hull does not deflect or damage the projectile (AP cap and windscreen are lost) and costs it at least 20% of its striking velocity at the smallest ranges where the lower armor deck might be penetrated (the velocity cost to penetrate the upper side hull armor increases as the angle of fall increases).

As mentioned previously, at the minimum angle of fall of 26^o to hit the near side's 4.33" (110 mm) sloped armor deck region through the 5.93" (151 mm) single-plate-equivalent KC n/A upper side hull armor the range is 29,000 yards (26,500 m) and the striking velocity is 1526 feet/second (465 m/sec). None of the flat portions of the lower armor deck can be pierced when hit at this range through either the weather deck or the upper side hull. At this angle of fall, the chance of hitting the sloped deck rather than the flat deck after penetrating the upper side hull theoretically almost exactly zero, since there is no leeway at all for vertical projectile motion. However, a real 14.96" projectile has an overlap zone where it is hitting both plates at once. This allows some chance of the projectile's nose prying the sloped and flat plates apart at the joint and punching through as discussed below.

At 26^o obliquity, after punching through the upper hull plate the value of V_r is 1212 feet/second (369 m/sec), the projectile's fuze has been set off and the AP cap and windscreen stripped off. The projectile has not been damaged or deflected, though. The slant distance to the upper edge of the sloped deck is 19.4' (5.9 m). At 1212 feet/second, a perfect 0.035-second delay gives 42.4' (12.9 m), so just under half of the delay time has been used up when the sloped deck is hit.

With a 68^o inboard slope from the vertical, the impact obliquity on the 4.33" plate is 42^o. For this thickness plate at that obliquity my pointed projectile formula gives an NL of 854 feet/second (260 m/sec) for the 38 cm projectile. Obviously, with a 1212 feet/second striking velocity, we completely penetrate, with an EX of 30.5^o and a new V_r of 860 feet/second (262 m/sec). The EX plus the 68^o inclination from the vertical make the projectile traveling at an effective angle of fall of 37.5^o. The 1.77" Ww torpedo bulkhead, which equals 1.68" Wh, would always be pierced. A perfect fuze delay would allow 13.8' (4.2 m) more before detonating inside the amidships protected space. Thus, if both sloped and flat plates are hit simultaneously, the sloped plate offers significantly less resistance due to its lower impact obliquity, even if it is thicker.

If the flat portion only is hit, the 3.15" lower armored deck cannot be penetrated after the upper side has been pierced until the angle of fall increases to 28.6^o (61.4^o obliquity on the deck) at 1509 feet/second (460 m/sec) at a range of 30,600 yards (28,000 m). At this range, the lower armor deck is only hit after the upper belt is pierced in a narrow 15.3' (4.7 m) wide strip from 15.3' to 30.6' (9.4 m) inboard from the near side (closer to the edge is only possible after the main belt is pierced and further inboard only after the weather deck is pierced). The 2.1' (0.64 m) portion of this strip nearest the side hull is actually hitting the upper end of the near side's 4.33" sloped deck area, which increases the chance of hitting the sloped area to 2.1/15.3 or 13.7% for a shell with a diameter of zero. A real 14.96" cylindrical projectile makes an oval hole 2.57' (30.9" or 0.79 m) wide at 28.6^o angle of fall (61.4^o obliquity), which is wider than the strip area hitting the sloped plate. Therefore, the projectile here is still overlapping both the flat 3.15" and sloped 4.33" plates. The 13.7% percentage thus means that this percentage of projectiles touches the slope, with some barely doing so and hitting on the 3.15" deck almost completely and some having the maximum 2.1/2.57 or 81.7% of their nose in the 4.33" plate. They completely penetrate here in either case, of course.

At a 28.6^o angle of fall, hits on the 118.25' (36 m) wide deck amidships through the weather deck only occur on a 69.9' (21.3 m) wide strip from the near edge of the weather deck to 48.4' (14.8 m) from the far edge - closer to the far edge will hit the far slope or miss the deck altogether - and the projectiles will hit the flat part of the lower main armored deck and pierce any part of it. The resolved ratio of the areas of the 3.15" vulnerable deck penetrated through the weather deck of 69.9' to that penetrated through the upper hull side of 15.3' is 18% side hull to 82% weather deck. The weather deck is thus seen as just over 4.5 times as likely as the upper hull to be randomly hit by a lower-deck-piercing, "vitals"-destroying projectile at this range. It follows that the chance of a random hit on the 4.33" sloped part of the lower armor deck instead of the flat 3.15" lower deck at this angle of fall through any part of the outer hull (weather deck or upper near side) is about 13.7% time 0.18 or about 2.5% of the combined 3.15" and 4.33" vulnerable deck areas (the chance is much, much less if the entire ship is considered).

Obviously, the small added vulnerable area on the sloped deck in the 29,000-30,600 yard range interval (26-28.6^o angle of fall) does not alter the vulnerability of the amidships region by much, but any increase in the chance of major ship engine, boiler, power, or fire-control damage due to penetrating hits in such vital areas is a cause of major concern to the ship's designers and crew! Until penetration through the weather deck path becomes possible at 30,700 yards (28.7^o angle of fall), the magazines would otherwise be completely invulnerable to the 38 cm projectile, so this 26-28.7^o angle of fall "sneak path" through the upper tip of the sloped deck is even more serious in this case - we are dealing with hits that can blow up the entire ship!

Due to the limited 30^o maximum elevation allowed the German 38 cm C/34 gun as mounted in the BISMARCK, the angle of fall of over 44^o required to hit the lower main armor deck's near side sloped area after hitting the weather deck is never reached, so no such hits can occur at a target angle of 90^o.

The 3.74" lower armored deck cannot be penetrated through the upper side hull until the angle of fall increases to 33.5^o at 1503 feet/second (458 m/sec) at a range of 33,900 yards (31,000 m). The NL of the 5.93" KC n/A-equivalent upper side hull plate at an obliquity of 33.5^o is 853 feet/second (260 m/sec), the EX was 33.49^o (obliquity 56.51^o on the 3.74" deck), and the V_r was 1156 feet/second (352 m/sec).

In the 29,000-33,900 yard interval between the ability to begin to penetrate the near side 4.33" sloped armor deck into the magazines to the ability to penetrate the exposed 3.74" main armor deck through the upper side we are only concerned about a small area - 35.4% of random upper hull hits at 33,900 yards will hit the sloped deck area which accounts for only 5.2% of the total vulnerable 3.74" and 4.33" deck areas from any outer area (upper side hull or weather deck) - but again we are not talking about minor damage, but total destruction of the ship from a magazine explosion! This subtle weakness is especially ironic due to the magazines having considerable additional flat deck armor weight expended to make them more invulnerable then other parts of the ship's hull. Note that though many of these hits would overlap both decks, even a small overlap can allow penetration to occur.

Let us compare the Citadel protection of a list of foreign contemporaries to the BISMARCK. These are the American USS SOUTH DAKOTA, the Italian VITTORIO VENETO, the British HMS KING GEORGE V, the French RICHELIEU, and the Japanese IJN YAMATO.

First, the following table gives quality factors needed to adjust the thicknesses of various kinds of homogeneous metals used in ship construction to a single 'equivalent STS plate" standard:

                                                                Ballistic Quality  
Homogeneous Metal Type                                                             

POST-WWI Homogeneous Krupp-Type Armor (Except Japanese NVNC &         1.00               
CNC)*                                                                              

Homogeneous Krupp-Type Armor Through WWI & Japanese NVNC & CNC        0.95               

British-Type 'DUCOL' ("D" OR "D.1") Improved High-Tensile             0.9                
Steel                                                                              

Homogeneous Cast Krupp-Type Armor (Special Fittings)                  0.9                

Homogeneous 'Nickel' Steel Armor from 1895 Through WWI                0.85               

Post-WWI High-Tensile Construction Steel ("HT" OR "HTS")              0.85               

High-Tensile Construction Steel Through WWI                           0.8                

Post-WWI 'Mild' OR 'Medium' Construction Steel                        0.78               

Homogeneous Nickel Steel Armor From 1899 To 1895                      0.75               

Mild or Medium Construction Steel from 1895 Through WWI               0.73               

Mild or Medium Construction Steel and Armor up to 1895                0.7                

Wrought Iron (Construction and Armor) (Solid Plates)                  0.6                

Cast Iron (Not Chilled or Otherwise Specially Treated)                0.4                

Multiply actual plate thickness to get effective U.S. WWII STS replacement thickness with roughly the same Navy Ballistic Limit.

* I am not singling out Japanese post-WWI armors for criticism. 'New Vickers Non-Cemented" (NVNC) armor, which is the homogeneous form of the face-hardened "Vickers Hardened" (VH) armor used in the IJN YAMATO, was deliberately kept at the level of late-WWI British armor due to the Japanese preoccupation with under-water hits. Just prior to WWII they introduced a new homogeneous armor "Molybdenum Non-Cemented" (MNC) that just met minimum U.S. Navy acceptance test standards and that seems to be similar to German Wh. It was used for most of the YAMATO's heavy homogeneous armor above the waterline while NVNC was used extensively for armor and anti-torpedo bulkheads below the waterline. Japanese "Copper Non-Cemented" (CNC) in several grades was very widely used during WWII as an NVNC replacement in thin plating, where its low nickel (a "strategic" metal in short supply) and high copper (available in large amounts to the Japanese and having limited nickel-like properties in some alloys) content did not cause its toughness to fall below minimum standards. Other nations did similar things during WWII, with various success, but the Japanese were more deliberate in writing their pre-WWII armor acceptance specifications to use such alternate armor alloys, rather than hurriedly reacting to short supplies of necessary alloying elements after they occurred, as other nations with less foresight did during WWII.

The SOUTH DAKOTA had a weather deck of 1.5" (38 mm) of STS and an upper side hull of one or two spaced layers of 0.625" (16 mm) STS - a 19^o outboard sloped extension of the internal armored bulkhead and, covering only the lower half of this upper hull side, an vertical extension of the lower hull. This region was generously spaced about 12' (3.7 m) high and floored by the main armor second deck at the top edge of the main side belt. This main armor deck was 5.3" (135 mm) of solid STS laminated to 0.75" (19mm) of STS in the outer 12' (3.7 m) of the deck and 5" (127 mm) STS laminated to 0.75" STS from there to the centerline. Over the amidships region of the ship, the decrease is due to a 1" (25.4 mm) upward vertical extension of the innermost anti-torpedo "holding" bulkhead joining the bottom of the main armor deck at that point and a 0.625" STS "splinter" deck spaced 3' (0.91 m) below the main armor deck covering the entire space between the two 1" bulkheads; this added spaced armor was considered heavy enough to allow a 0.3" (8 mm) decrease in the main armor deck where both the armor deck and this inner vertical bulkhead or the splinter deck would be hit. There was an additional 0.3" (B mm) mild steel deck spaced about 10' (3 m) below the splinter deck, but this would not mean much if the projectile got through the rest of the deck armor and detonated or even if the projectile was rendered inert and still had any significant remaining velocity. However, over the magazines the splinter deck was eliminated and this third deck was thickened to a solid 1" STS magazine shield as well as increasing the inner holding bulkhead extension to 1.5" (38 mm), which will stop most explosive effects and fragments of the German 38 cm AP projectile if it explodes properly a short distance away - this 1.5" layer was even added between the magazines and amidships areas. This would prevent an amidships hit from putting fragments into the magazine (which is a strong candidate for the cause of the demise of HMS Hood).

To add laminated (partially reinforcing) plates together, I simply split the difference between (1) adding up their effective thicknesses (each plate's thickness after multiplying it by a quality factor based on armor type) as though they were fused into a single plate and (2) applying the spaced (totally independent) plates armor formula discussed with the BISMARCK's steering gear armor to these effective thicknesses. The quality factor for STS and most related WWII armor steels is 1.00, so their effective thickness equals their actual thickness. The 5" plus 0.75" central deck area is thus equal to the average between a 5.75" (146 mm) single STS plate and its spaced array value of 5.25" (133 mm), which gives 5.5" (140 mm) when they are laminated together. Similarly, the 5.3" plus 0.75" outer deck is equal to one 5.8" (147 mm) STS plate.

These thin upper side hull plates only reduce the velocity of the 38 cm projectile by a small 15-35 feet/second (4.6-10.7 m/sec), even if both are penetrated. They would not decap the projectile and, at a Target Angle of 90^o, they require an angle of fall of at least 22^o to set off the base fuze, even if both plates are hit.

If the angle of fall is greater than about 37^o, a hit on the upper side hull will always hit the outboard armor deck region; to hit the inboard region requires going through the weather deck first. This is also the minimum angle of fall for a weather deck hit to reach the near side outer deck region. For the BISMARCK's 38 cm gun, 37^o is at 36,100 yards (33,000 m). Hitting the outer deck region rather than the inboard deck region means little over the amidships part of the ship. At least 1.25" (32 mm) STS is needed to stop all 38 cm AP projectile fragments and blast. Only outside of the magazines does the 1.5" STS inner bulkhead protect from hits that penetrate the outer main armor deck and detonate prior to hitting this bulkhead. This thickness extends down 13' (4 m) to the level of the 1" STS magazine roof, below which it thins down to its anti-torpedo thickness of 0.75" (19 mm) HTS (quality factor 0.85), which equals 0.64" (16 mm) of STS.

The 1.5" weather deck cannot deflect the 38 cm projectile, but it could decap the projectile and set off its base fuze. For the 5.5" central deck region, my data indicates that the minimum range for a 38 cm projectile to barely completely penetrate that deck after going through the weather deck is 35,500 yards (32,500 m) at an angle of fall of 36.5^o and a striking velocity of 1503 feet/second (458 m/sec) (the 38 cm gun's minimum striking velocity). The 5.8" outer deck region has a minimum range of 36,600 yards (33,500 m) at the same striking velocity and 37.7^o angle of fall through the weather deck.

Note how near this is to the maximum gun's 39,000 yard (35,700 m) range at a 41.5^o angle of fall and 1512 feet/second (461 m/sec) striking velocity due to the BISMARCK's 30^o maximum allowed turret gun elevation! In fact, if we use this maximum range, after penetrating the weather deck and losing 32 feet/second (9.7 m/sec) velocity as well as its AP cap and then piercing the 5.8" deck, EX is only 4.9^o and V_r is 687 feet/second (209 m/sec), which means that the projectile cannot penetrate the inner bulkhead and will move on the average 15.6 feet (4.8 m) before being blown up by its fuze. Note that the deflection is over 45^o, so the projectile is probably tumbling and almost all of its length would usually be above the 1.5" bulkhead when it goes off. At the 1.5" STS/0.75" HTS bulkhead joint the 1" (25.4mm) STS third deck magazine roof continues outboard to the belt, forming the top of the inner void in the anti-torpedo system. This plate would stop or slow down a yawed or sideways-moving projectile at such a low velocity, so penetration to the 0.75" HTS bulkhead level is even less likely. The 5.8" deck is therefore proof against the 38 cm gun unless the fuze delay is well over its design length and an intact, tumbling projectile hits just right to pierce the void's top plate. Unlikely!

To completely penetrate the 5.8" near side outer deck through the upper side hull, the minimum range is 36,400 yards (33,300 a), the striking velocity is 1503 feet/second (458 m/sec), and the angle of fall is 37^o. About 25% of hits here at this range or more would hit the top edge of the 12.2" belt where it overlaps the deck. Only above 38,200 yards (34,900 m) and 39.9^o angle of fall does the deflection angle go below 45^o, so only in the last 800 yards of the gun's entire range was there a reasonable chance of a 38 cm AP shell penetrating the 1" third deck.

The 5.5" inner armor deck can be pierced through the upper side hull at a minimum range of 35,000 yards (32,000 m) with an angle of fall of 35.1^o and 1503 feet/second striking velocity. This path is pinched off at 36,100 yards, above which only the 5.8" deck is hit.

The RICHELIEU had a weather deck and top 7.25' (2.2 m) of its upper side hull of 0.2-0.28" (5-7 mm) of high tensile steel. The second deck and lower 10.8' (3.3 m) of its upper side hull were both circa 1" (25.4mm) of high tensile steel. The third deck was the main armor deck of homogeneous armor steel resting on the upper edge of the main side belt armor. It was 5.91" (150 mm) thick over the amidships area and 6.69" (170 mm) over the magazines. Spaced about 7.25' below the main armor deck was another 1.57' (40 mm) homogeneous armor deck covering about 75% of the center region over both the engines, boilers, and magazines, with the outer 25% being a sloped 1.97" (50 mm) deck meeting the bottom of the recessed main side belt at an angle of about 50^o from the horizontal, much like the lower deck armor of the HMS HOOD. Below the 1.97" sloped deck region was the ship's fuel and anti-torpedo system, with several thin high tensile steel vertical bulkheads, the thickest being 1.18" (30 mm) thick with several feet of liquid fuel in front of it.

The analysis of the USS SOUTH DAKOTA is repeated here for the Richelieu's 5.91" main deck. The 1.97" sloped lower deck is so close to the side belt that any penetrations of the main armor deck next to its near edge will have to be with an angle of fall of at least 36^o (see below) and even if the hit penetrated the main armor deck and the 1.97" sloped deck, it would be going almost straight down and would detonate inside the liquid part of the anti-torpedo system or, if a dud, go out the ship's bottom below it. The liquid layer and the several spaced inboard anti-torpedo bulkheads would probably contain all blast and fragments, so such a hit would cause relatively minor immediate damage in most cases. (Such damage can cause indirect effects however, as the lower hull hits on the BISMARCK by the PRINCE OF WALES illustrate.)

The 1" second deck or lower part of the upper side hull would only reduce the striking velocity on the main armor deck by about 35 feet/second (10.7 m/sec) and would not decap the 38cm projectile, unlike the heavier upper side of the SOUTH DAKOTA. The 1" plating would set off the fuze of the projectile if hit at over about 15^o obliquity - always for a deck hit and at over 20,800 yards (19,000 m) against the side. The 5.91" portion of the main armor deck can be pierced by the German 38 cm gun starting at 35,300 yards (32,300 m) with an angle of fall of 36^o degrees and a striking velocity of 1503 feet/second (458 m/sec), which is the minimum striking velocity for that gun. However, just penetrating the main armor deck is not enough, since the 1.57" flat lower deck can stop most blast and fragments of a detonating projectile. My computations indicate that the range must increase until the angle of fall is 37.7^o at 36,600 yards (33,500 m) with the same striking velocity to have enough remaining velocity to pierce the 1.57" lower deck, which requires a V_r of about 275 feet/second (83.8 m/sec) after exiting the bottom of the main armor deck with an EX of under 1^o - the deflection is over 45^o and therefore penetration is doubtful. The SOUTH DAKOTA's outer magazine armor is thus much like RICHELIEU amidships.

The RICHELIEU's 6.69" portion of the main armor deck over the main magazines may barely be penetrable at the extreme range possible with the German 38 cm gun as mounted in the BISMARCK, but the German penetration tables give it exactly at maximum range, which is hard to call. The 1.57" flat lower deck is absolutely impenetrable, so the magazines are proof against a deck hit from this gun.

Note that the very thin weather deck and the top portion of the upper side hull of this French ship are too thin to initiate the base fuze of a battleship-caliber projectile, so the two-deck distance between the weather deck and the main armor deck is, at most, only really a single-deck distance, since the 1" lower portion of the upper side hull is marginal in thickness for setting off such fuzes. It takes at least 1.05" (27 mm) of steel to make sure that all 38 cm projectile base fuzes that are not duds are set off under all conditions. These details do nothing to reduce the very good deck protection afforded the RICHELIEU against any battleship weapon.

The British HMS KING GEORGE V had the simplest armor arrangement of all post-WWI battleships. Most of the load-bearing portions of the ship consisted of British Ducol ("D" or "D.1") extra-high-strength Silicon-Manganese high-tensile construction steel. D-steel was a very high grade construction and light armor material that was developed in the early 1920's by the British Colville Company and also used extensively by the Japanese and, if the Italians copied British practice as they did in many other things, by the Italians. It did not use many expensive toughening and hardening alloy elements like nickel or chromium or molybdenum to achieve its strength, but instead used a good knowledge of the interaction between the relatively cheap toughening/hardening elements silicon and manganese when properly combined with a high-quality low-carbon steel alloy.

The KING GEORGE V's weather deck was made up of 1.2" (31 mm) D-steel in two laminated layers, one, I believe, of 0.5" (13 mm) thickness and the other of 0.7" (18 mm) thickness, which give an effective single-plate thickness of 1.09" (28 mm) D-steel or 1" (25 mm) of STS. A narrow band consisting of a single 0.5" D-steel thickness equal to 0.45" (11 mm) of STS was used near the centerline over an unknown length of the Citadel. The weather deck was spaced above the main armor second deck, which rested on the upper edge of the main side belt armor, by 8.25' (2.5 m) with the upper side hull being a single thickness of D-steel 0.75-1" (19-25 mm) thick, which equals 0.675-0.9" (17-23 mm) of STS, with the 1" thickness covering all but the extreme lower edge of the upper side hull. These thicknesses are not enough to deflect or decap the German 38 cm projectile and, as mentioned previously, will not slow the projectile down by more than 15-35 feet/second (4.6-10.7 m/sec) at most. The weather deck would set off the projectile's base fuze at all impact angles, except for that narrow centerline thickness, where an obliquity of greater of 55^o was needed, which meant an angle of fall of under 35^o - with the German 38 cm gun a range under 35,000 yards (32,000 m). The 1" upper side hull would set off the 38 cm projectile base fuze at a Target Angle of 90^o only when the angle of fall was over 12^o - with the 38 cm gun at a range over 8,700 yards (8,000 m), assuming that the fuze acts exactly like U.S. WWII fuzes, as previously discussed.

The 8.25' space between the weather deck and the main armor deck would only provide about 49' (14.9 m) slant distance even at the minimum angle of fall of 10^o for a projectile penetrating the weather deck. This means that most WWII armor-piercing projectiles would reach and penetrate the main armor deck, if they are able to, prior to their base fuze setting them off -- the inter-deck gap is therefore not an important part of the protection.

The honeycombed armored gratings extending over the funnel uptakes at the main armor deck level had a 1.96" (50 mm) "Non-Cemented Armor" (NCA) STS-type vertical cylinder enclosing them for several feet above that deck to increase the protection against low-angle fire from the sides. This plate would always decap the projectile and, if not already done, set off the projectile's base fuze. Decapping the projectile would increase the chance of ricochet at high obliquity, but activating the fuze would have nil effect on the ship's protection. I would assume that the armored gratings were roughly equal to the main armor deck in effective thickness, but I do not have information on their design details. The gratings would have to be about 13" (33cm) of NCA (or equivalent) to equal the ship's amidships deck armor thickness (see below).

The second deck had essentially all of the deck protection afforded the ship. It consisted of a single thick NCA plate of 4.88" (124 mm) thickness amidships laminated to a single 0.5" D-steel support plate, giving a effective thickness of STS or NCA of 5.17" (131 mm). Over the magazines at each end of the Citadel the NCA plate increased in thickness to 5.87" (149 mm) over the same 0.5" of D-steel, giving an effective STS or NCA thickness of 6.15" (156 mm). There were no protective decks below the main armor deck, though the lower extension of the barbettes was composed of 2" (51 mm) of NCA that isolated them from external explosions (or, more likely, was designed to isolate the magazines from explosions inside the barbette, given the traumatic British WWI experience with turret explosions passing into the magazines and blowing up British ships); the Japanese followed this practice to the letter in their IJN YAMATO.

The KING GEORGE V's main armor second deck could be penetrated by the German 38 cm gun at a range of 33,200 yards (30,400 m) over the amidships engine and boiler rooms or at 36,600 yards (33,500 m) over the main magazines. The striking velocity and angle of fall is 1509 feet/second (460 m/sec) and 32.5^o for the amidships deck and 1503 feet/second (458 m/sec) and 37.7^o for the magazine deck. This is not much different from the USS SOUTH DAKOTA or RICHELIEU, but far better than the BISMARCK!

The Italian VITTORIO VENETO has about the most complex armor arrangement of any warship ever built when one considers how many armor plates a projectile may pass through with some trajectories! The weather deck consisted of 1.42" (36 mm) of "Piastre Omogenee' (PO) STS-type homogeneous armor laminated to a 0.35" (9 mm) support plate of "Elevata Resistenza" (ER) high-tensile construction steel, which I believe was a form of British D-steel (quality factor 0.9), giving an effective STS or PO single-plate thickness of 1.64" (42 mm). There was a rather narrow 7.5' (2.3 m) vertical space and then an unarmored second deck of 0.47-0.55" (12-14 mm) ER (which contributes virtually nothing to the ship's deck protection) and then another 7.5' space to the main armor third deck. The vertical upper side hull of this 15' (4.6 m) space was a single 2.76" (70 mm) thickness of PO. The outer armor would both decap and set the base fuze off of any incoming projectile. Decapping the projectile would increase the chance of ricochet at high obliquity. Unlike the BISMARCK, the weather deck plate is still thin enough so that my formulas say that the projectile is not deflected at any angle of fall, including the minimum 10^o value at a range of 15,990 yards (14,500 m) and a striking velocity of 1886 feet/second (575 m/sec) that my formulas allow any horizontal deck to be penetrated; the NL for the 1.64" STS-equivalent weather deck at 80^o obliquity is 1017 feet/second (310 m/sec) according to my eyeball extrapolation of the German 38 cm homogeneous armor penetration tables in G.Kdos. 100.

The two-deck space in this ship where the projectile's fuze might prematurely terminate its flight before reaching the main armor deck is somewhat narrower than the BISMARCK, but wider than most other ships (except for the IJN YAMATO). As with the BISMARCK, only at very shallow angles of fall would this have much effect due to the rather long delays used in WWII armor-piercing projectiles; the 15' vertical distance gives 86.4' (26.3 m) slant distance from the near edge of the weather deck to the main armor deck at 10^o angle of falls which is long enough to allow almost all German 38 cm projectiles that were not out-and-out duds to destroy themselves prior to reaching the main armor deck after a weather deck hit. The range where the slant distance between the weather and main armor decks equals the distance that the projectile could move if it had an exact as-designed 0.035-second fuze delay is 21,200 yards (19,400 m) at an angle of fall of 15.5^o and a striking velocity of 1699 feet/second (518 m/sec). G.Kdos. 100 gives an NL for the 1.64" weather deck plate of 522 feet/second (159 m/sec) at this angle of fall, which in turn gives a V_r of 1617 feet/second (493 m/sec) after penetrating the 1.64" weather deck and a 56.6' (17.3 m) slant distance to the main armor deck. Roughly half of the non-dud German 38 cm projectiles would not reach the main armor deck after a weather deck hit except in pieces at this range, with the percentage of projectiles reaching the main armor deck intact decreasing as the range decreases.

The main armor deck of the VITTORIO VENETO is complex. The central 60% of the deck measured from the centerline outward was 3.94' (100 mm) PO laminated to 0.47" (12 mm) ER over the amidships region and 5.91" (150 mm) PO laminated to 0.47" ER over the magazines at each and of the Citadel, giving a single-plate STS or PO equivalent of 4.21m (107 mm) amidships and 6.17' (157 mm) over the magazines. The outboard 40% of the deck evenly divided on both sides of the ship from the upper edge of the main armor belt inward was at a somewhat reduced thickness of 3.54" (90 mm) PO laminated to 0.35" (9 mm) ER, which gives an STS or PO equivalent of 3.74" (95 mm) (the BISMARCK magazine main armor deck thickness) amidships, and 3.94" (100 mm) laminated to 0.35" ER, which gives an STS or PO equivalent of 4.14" (105 mm) over the magazines. The 40% inboard distance is 21.6' (6.6m) inboard from each side of the ship and represents the point where the under side of the main armor deck meets the top edge of the last inboard inclined splinter screens behind the main belt armor, a 0.94" (24 mm) PO plate inclined inboard (top closer to centerline than the bottom) 30^o from the vertical.

Note that this deck armor thickness arrangement is the opposite of that used in the USS SOUTH DAKOTA which had the outer deck region the thickest. The Italians simply added up the effective-plate thicknesses of the deck and the 0.94" splinter plate and shaved the outer deck until it and the inner deck region gave the same weight of armor to be passed through. This logic has some major flaws! Outboard of the 0.94" plate, damage would be primarily to non-essential spaces, if the projectile's filler explosion effects and its fragments cannot pierce the 0.94" plate. However, the 0.94" plate would not stop many of the fragments and, through the holes made by these fragments, incendiary material from a large-caliber projectile explosion such as the German 38 cm projectile would cause, so the division is rather weak unless the projectile is a dud or only undergoes a low-order explosion that the 0.94" plate can contain. Also, if the projectile was a dud, it has a much greater chance of hitting the 0.94" bulkhead and piercing it due to its 30^o inboard inclination reducing impact obliquity and its thinness. Thus, the concept of reducing the deck armor where additional plates are spaced behind it is not a good idea unless the last plate in the series can contain blast and fragments from an exploding projectile if it fails to get all of the way through the protection system.

With the VITTORIO VENETO's armor deck/splinter plate design, only if the projectile that pierced the main armor deck above the anti-torpedo system was deflected almost straight downward and the fuze delay allowed it to move the circa 19' (5.5 m) distance (plus the projectile's body length) required to imbed itself in the liquid-filled portion of this system surrounded by its 1.57" (40 mm) ER holding bulkhead would containment of its blast and fragments be possible. This is a not highly probable with the German 38 cm projectile considering how much the main armor deck would slow down the projectile and shorten its travel during its delay if it hit at a low enough velocity to be deflected, while if it penetrated at a higher velocity it would not be deflected as much and has a good chance of hitting the 0.94" plate rather than the top of the Pugliese holding bulkhead.

Note that there were two of these splinter plates reaching from the top of the Pugliese anti-torpedo system's main curved holding bulkhead to the underside of the main armor deck. The second was the 0.94" plate mentioned above. The first was spaced about 4' (1.2 m) behind the main armor belt and inclined 8^o outboard parallel to it and was made up of 1.42" (36 mm) PO. It was this plate that was strong enough to contain essentially all of the blast and fragments of a 38 cm armor-piercing projectile explosion, especially when backed up by the second 0.94" plate mentioned above, but only an upper side hull hit just above the main armor deck (an 18.5% chance if hits are random an the upper side hull) would ever hit this 1.42" splinter plate and, even if this occurred, this splinter plate would only be useful if the projectile barely penetrated the main armor deck and could not penetrate the thin splinter plate, too.

If the Italian designers had swapped the 0.94" and 1.42" splinter plates, the decrease in the outboard deck armor would have been much more justifiable, though still a poor idea, especially around the magazines where the 6.17" inner main armor deck was close to invulnerable to the BISMARCK's gun, as will be seen below.

Even at its thinnest, the main deck armor of this Italian battleship is equal to the heaviest main deck armor on the BISMARCK and most of it is noticeably heavier than the BISMARCK's deck armor. Also, the premature deflection effect due to the weather deck that compromises the BISMARCK's amidships deck armor does not occur on the VITTORIO VENETO.

To hit the near side's outboard main deck region at a Target Angle of 90^o after hitting the weather deck requires an angle of fall of at least 34.8^o; at a closer range the projectile can only hit either the inboard or far side outboard main deck region. With the German 38 cm gun this occurs at a range of 34,800 yards (31,800 m) with a striking velocity of 1503 feet/second (458 m/sec), the minimum possible striking velocity. Above this angle of fall, a hit on the upper side hull always hits the near side's outboard armor region, with an 18.5% chance of this being outboard of the 1.42" splinter plate under the deck, which increases the protection after a deck penetration noticeably.

The 1.42" outer splinter screen, when coupled to the 0.94" inner splinter screen, virtually eliminates direct damage to the ship's inner "vitals" if the projectile detonates in the 4' (1.2 m) space between it and the main armor belt or in the liquid-filled Pugliese anti-torpedo system below it bounded by its 1.57" (40 mm) curved inner holding bulkhead. Therefore, this 4' on the far side of the ship can be eliminated from the ship's vulnerable width, as can the width of the main belt armor system (the near side 1.42" plate can be punched through by a battleship caliber projectile unless the remaining velocity is very low after penetrating the main armor deck). As a result the ship amidships hull has only roughly 99' (30.2 m) of vulnerable width at a Target Angle of 90^o.

Portion Of Main Armor Deck  Minimum Range After         Minimum Range After         
Hit  (STS Equivalent        Penetrating Through Upper   Penetrating Through         
Thickness)                  Side Hull                   Weather Deck                

Outer Deck Amidships        31,000-Maximum*             30,300-Maximum**            
(3.74")                                                                             

Inner Deck Amidships        32,000-34,800               32,200-Maximum              
(4.21")                                                                             

Outer Deck Magazines        31,700-Maximum*             31,800-Maximum**            
(4.14")                                                                             

Inner Deck Magazines        No Penetration              37,500-Maximum              
(6.17")                                                                             

1) Ranges given in yards (multiply by 0.9144 for meters).

2) 38 cm C/34 gun firing 38 cm Psgr. m. K. L/4,4 projectiles has a maximum range of 39,000 yards (35,700 m).

3) At these ranges, the 15'-high (4.6 m) upper side hull covers less than 20% of the vulnerable deck area, almost all of which is in the near side outer armor deck region.

*Near side only. Far side cannot be hit through side hull at over 10^o angle of fall, which is reached at 15,600 yards (14,300 m), even if fuze delay were to be ignored.

**Far side only. Near side cannot be hit through weather deck at under 34.8^o angle of fall, which is reached at 34,800 yards (31,800 m). This range is also the maximum range that either inner deck region can be hit through the side hull.

Through the 2.76" upper side hull armor, the inboard main armor deck regions could be penetrated as follows:

(1) Complete penetration of the amidships inboard 4.21" STS-equivalent deck through the 2.76" upper side hull occurs at a striking velocity of 1506 feet/second (459 m/sec) and an angle of fall of 30.8^o (a 59.2^o impact obliquity), giving a range of 32,000 yards (29,300 m). The 2.76" plate hit at 30.8^o obliquity has an NL of 417 feet/second (127 m/sec) and a V_r of 1447 feet/second (441 m/sec) for the decapped projectile. At this angle of fall, the worst case slant distance from the upper side hull impact point and the main armor deck is 29.2' (8.9 m) and at 1447 feet/second, a 0.035-second delay gives 50.6' (15.4 m) so that very few projectiles will not reach the main armor deck due to the fuze delay. Only a hit on the upper 14.2%, measured from the weather deck down, of the upper side hull will hit the inboard amidships region at this angle of fall, the rest will hit the near side outboard deck region. This percentage drops nearly linearly to zero as range and angle of fall increase to 34.8^o and 34,800 yards (31,800 m), respectively. This small 2800-yard-wide (2560 m) "window" is the only time that the amidships (engines and boilers) inboard portion of the main armor deck can be penetrated after hitting the upper side hull - below this range hits do not penetrate and above it they cannot occur at a Target Angle of 90^o because the projectile would hit the outboard deck area instead.

(2) Penetration of the magazine inboard 6.17" STS-equivalent deck cannot be done because at the required angle of fall to reduce impact obliquity enough for penetration the projectile would hit the near side outboard armor deck region instead.

Through the 1.64" STS-equivalent weather deck the inboard main armor deck regions could be penetrated as follows:

(1) The penetration range for the 4.21" amidships inboard armor deck (engines and boilers) was 32,200 yards (29,400 m) where the angle of fall was 30.9^o (a 59.1^o impact obliquity) and the striking velocity was 1506 feet/second (459 m/sec). The weather deck NL was 439 feet/second (134 m/sec) and V_r was 1440 feet/second (439 m/sec).

(2) Similarly, through the weather deck the penetration range for the 6.17" magazine inboard armor deck was 37,500 yards (34,300 m) where the angle of fall was 39.3^o (a 50.7^o impact obliquity) and the striking velocity was 1506 feet/second (459 m/sec). The weather deck NL was 371 feet/second (113 m/sec) and V_r was 1461 feet/second (445 m/sec).

Hits on the far side outer armor deck region through the near side upper hull at close range will always ricochet off if they reach that deck area, but will rarely reach it due to fuze action blowing up the projectiles first.

Hits an the near side outer main armor deck through the 2.76" upper side hull can completely penetrate as follows:

(1) The amidships outboard 3.74' STS-equivalent deck will be penetrated at a striking velocity of 1506 feet/second (459 m/sec) and an angle of fall of 28^o (a 62^o impact obliquity), giving a range of 30,100 yards (27,500 m). The upper hull plate is hit at 28^o obliquity which gives a NL of 412 feet/second (125 m/sec) and a V_r of 1449 feet/second (442 m/sec) for the decapped projectile.

(2) Similarly, the magazine outboard 4.14" STS-equivalent deck will be penetrated at a striking velocity of 1506 feet/second (459 m/sec) and an angle of fall of 30.4^o (a 59.6^o impact obliquity), giving a range of 31,700 yards (29,000 m). The upper hull plate is hit at 30.4^o obliquity, which gives a NL of 413 feet/second (126 m/sec) and a V_r of 1448 feet/second (441 m/sec) for the decapped projectile.

Through the 1.64" STS-equivalent weather deck, the outboard main armor decks can be pierced as follows (note that the near side outer armor deck cannot be hit through the weather deck until the angle of fall increases to 34.8^o at a range of 34,800 yards (31,800 m), so these numbers are for the far side outboard main armor deck only):

(1) The 3.74" amidships outboard armor deck could be pierced at a range of 30,300 yards (27,700 m) at an angle of fall of 28.4^o (a 61.6^o impact obliquity) and a striking velocity of 1511 feet/second (461 m/sec). The weather deck had a NL of 486 feet/second (148 m/second) and V_r was 1429 feet/second (436 m/sec).

(2) Similarly, the 4.14" magazine outboard armor deck could be pierced at a range of 31,800 yards (29,100 m) at an angle of fall of 30.5^o (a 59.5^o impact obliquity) and a striking velocity of 1508 feet/second (460 m/sec). The weather deck had a NL of 446 feet/second (136 m/second) and V_r was 1440 feet/second (439 m/sec).

Note that all of these decks except for the 6.17" inboard main armor deck are penetrated at pretty close to the same range, with a spread of only a couple of thousand yards. However, the 0.94" splinter plate was not thick enough to stop the blast and fragments of a battleship-caliber projectile when it exploded as designed. Therefore, the thinning of the main armor deck outboard of this plate greatly increased the danger to the magazines. Using the 1.42" splinter plate in place of the 0.94" plate would have helped the magazine protection, though neither plate would stop a direct hit most of the time. As it was, only in the 4' gaps between the armor belts and the 1.42" splinter plates would the projectile's blast and fragments be stopped and only then if the projectile could not penetrate the 1.42" plate after passing through the outer main armor deck through the near side upper hull (a weather deck hit could never hit the near side 1.42" splinter plate). (A far side hit in the 4' gap on that side through the weather deck was not a problem.) Up to a range of 37,000 yards (33,806 m), where the striking velocity was 1503 feet/second (458 m/sec) and the angle of fall was 37.8^o, the 1.42" near side splinter plate would confine the projectile after the 4.14" outboard magazine main armor deck was pierced - a 6,300 yard (5,760 m) improvement in magazine protected range! Similarly, for the 3.74" outboard amidships main armor decks the maximum range was 34,400 yards (31,506 m), the angle of fall was 34.9^o, and the striking velocity 1506 foot/second (459 m/sec) for projectile confinement - a 1300 yard (3,930 m) amidships range improvement. The projectile would be going essentially straight down at over 900 feet/second (274 m/sec) at this maximum range, so if the projectile delay was anything but extremely short, it would reach the top of the 1.18-1.57" (30-40 mm) Pugliese holding bulkhead, pierce it, and blow up inside the anti-torpedo system, where its explosion would also be contained by the liquid and the holding bulkhead. Thus, in all cases where the 1.42" plate confined the projectile, it greatly enlarged the outer protected range limit for deck hits. Reducing the outboard magazine main armor deck thickness thus was not compensated by the 0.94" splinter plate, but it would have been at least partly justified if the 1.42" plate been used instead. A design flaw.

The Japanese IJN YAMATO had an armored third deck with a 7.87" (200 mm) flat central deck and a 9.06" (230 mm) sloped outer region that took up about 25% of the deck area from each of the side edges. The main armor deck was set at the top edge of the main armor belt and the slope connecting the 7.87" flat central region to the belt edge was only 8^o from the horizontal and lifted the armor deck slightly to allow the boilers and engines more space. This deck was made of Japanese Molybdenum Non-Cemented (MNC) homogeneous armor (slightly inferior to U.S. STS, but not by much) and were totally proof against a deck hit from the German 38 cm gun. Even the funnel uptake armor grating plate, which was drilled through with many holes to allow the stack gases to pass through the armored deck and was thus only equal to about 40% of its actual thickness of solid MNC armor without holes, was 14.96" (380 mm) thick, giving a 6" (152 mm) effective thickness. This grating is surrounded by a cylindrical 1.97" (50 mm) homogeneous CNC armor plate wrapped around the raked funnel base and rising several decks into the superstructure, which is a unique armor arrangement used in these ships only. For the BISMARCK's gun projectile to reach the grating through the weather deck at an obliquity where penetration is worth calculating requires passing through a lot of superstructure bulkheads and decks that would probably reduce the striking velocity somewhat, but this is hard to determine (I am going to use the full 1.97" thickness of the grating shield instead of reducing it by 5%, which I would normally do with CNC, because of this).

The YAMATO's flat middle deck region (with the grating at its center over the boilers) could only be reached from above after passing through two lightly armored decks spaced 8.5' (2.6 m) apart and 8.5' above the main armor deck or from the side through a lightly armored upper hull side 17' (5.2 m) high. The upper two decks and upper side hull were made of single plates or two laminated plates of British-type D-steel, which I give a quality factor of 0.9, as given in the table above. The plates were arranged so that they were thickest at the hull side for the decks and thickest at the top of the upper side hull. This meant that the more steep the angle of fall and, thus, the slower the attacking projectile was going, the thinner the upper hull or deck plating that was hit near the centerline, allowing the plates near the side that would be hit at more shallow angles of fall by more rapidly moving projectiles to be reinforced considerably. Incidentally, this also was the best arrangement for strengthening the ship for bad weather, since heavy waves would bear down mostly near the ship's side. The weather deck had only 0.5" (13 mm) D-steel at the centerline, giving an effective STS thickness of 0.45" (11 mm), but this increased in regular steps to 1.42' (36 mm) at the hull side edge, made up of two laminated plates 0.79" (20mm) over 0.63' (16 mm), giving an effective D-steel thickness of 1.29" (33 mm) and an effective STS thickness of 1.16" (30 mm) at its thickest. The second deck only used single plates and it started out at the centerline at 0.39" (10 mm) - equaling 0.35" (9 mm) of STS - and gradually thickened to 1" (25 mm) - equaling 0.9" (23 mm) STS - for the 25% area directly above the outer sloped portion of the main armor deck. The lower half of the upper side hull between the second and third decks was made of a 0.31" (9 mm) D-steel plate laminated to a 1" D-steel plate, giving an effective D-steel thickness of 1.22" (31 mm) and an effective STS thickness of 1.1" (28 mm). The upper half of the upper side hull between the weather (first) and second decks was made of a 0.71-0.87" (18-22 mm) D-steel plate laminated to a 1" D-steel plate, giving an effective D-steel thickness of 1.56-1.7" (40-43 mm) and an effective STS thickness of 1.4-1.53" (36-39 mm).

This plate arrangement would always set off the 38 cm projectile's base fuze, usually on the first plate hit, but only the outer edge of the weather deck or upper half of the upper side hull would decap the projectile.

The 6"-effective-STS-thickness armored grating seems to be a design fla