The following are the set of assumptions used to reconstruct the engagement:
1) U.S. Mk 23 torpedoes run at 46 knots (77.68 feet/sec.)
2) Mk 23 torpedo will leave the tube at 30 knots (50.66 feet/sec.)
3) Upon leaving the tube, the torpedo will move forward on a straight line for 120 feet to avoid making a turn into Cavalla's bow.
4) Thereafter, the torpedo will continue accelerating and begin turning to its final heading. It will accelerate to 90% of full speed within 6 seconds, and up to full speed within 8.4 seconds (per conversation with F. Milford).
5) Cavalla is traveling at 3 knots (5 feet/sec.) on course 025 True.
6) Torpedoes are fired at 8-second intervals (per Cavalla's log), leading to a 40-second firing sequence, with torpedo launches at T=0, 8, 16, 24, 32, and 40 seconds. Cavalla will move roughly 200 feet forward during this time interval.
7) Torpedoes are fired on the following bearings:
#1 fired with 107 track angle, gyro 017 (042 True)
#2 fired with 110 track angle, gyro 020 (045 True)
#3 fired with 120 track angle, gyro 030 (055 True)
#4 fired with 112 track angle, gyro 022 (047 True)
#5 fired with 134 track angle, gyro 044 (069 True)
#6 fired with 122 track angle, gyro 032 (057 True)
8) Shokaku is moving on course 115 True, at a speed of 25 knots (42.22 feet/sec.)
9) Estimated "wander" (the amount a torpedo will vary from its initial course track) for a Mk 23 torpedo over a range of 1,200 to 1,500 yards is assumed to be negligible (per conversation with F. Milford), and will be a matter of a few feet.
10) Shokaku will not slow appreciably during the course of this engagement, even though her power may be knocked out. Shokaku is a large ship, and her momentum is assumed to carry her through the engagement at nearly constant speed.
11) Shokaku is assumed to not take any evasive action during the course, and will not make any course changes. It is unlikely in any case that a course change would have had any effect during at least the first sixteen seconds of the engagement, which is when the critical torpedoes strike home. One source in the Japanese record does mention beginning a turn to comb the wakes, but makes it clear that this action was too late to work.
U.S. Naval Technical Mission to Japan, "Reports of Damage to Japanese Warships - Article 3, Japanese Records of Major Warship Losses", Index No. S-06-3, January 1946.|
This source describes damage and sinkings of Japanese warships in two different sections that are very similar, but differ in minor details.
The first section is a series of 'capsule reports' that were compiled from interviews of naval designers and constructors from the Japanese Naval Ministry, written reports from the Naval Ministry, and various USSBS interrogation reports. The personnel interviewed included Technical Rear Admiral Yagasaki [Masatsume] and Technical Captain Inagawa, ex-IJN, of the Design Branch, Fourth Section (Ship Construction), Technical Department, Japanese Naval Ministry. These men were especially knowledgeable of the design and construction details of the Japanese aircraft carriers and had participated in the panels that investigated sinkings of many Japanese carriers."
For SHOKAKU, it reads:
The second part of S-06-3 includes what is termed Enclosure (A), "Second Repatriation Department, Historical Survey Section, Japanese Government Report to NavTechJap, dated 15 December 1945. It is stated as being "based almost entirely on Japanese Naval Action Reports, submitted by the Commanding Officer or by the Senior Surviving Officer (as the case might be) for the various ships. It was submitted to NavTechJap in the Japanese language and translated by U.S. Naval Officers (Japanese Language Officers) assisted by civilian employees (Japanese Nationals) of NavTechJap." It can be considered as a brief of official Japanese naval action reports.
The Enclosure A entry for Shokaku reads:
Hajime Fukaya, (edited by Martin E. Holbrook); "The Shokakus - Pearl Harbor to Leyte Gulf", U. S. Naval Institute Proceedings, June 1952, pp. 638-641.|
Fukaya relates that "The first blow came from an unexpected source. At 2:01 P.M. on June 19, 1944, the Shokaku while 140 miles north of Yap Island was torpedoed three times by the U.S. submarine Cavalla. Damage to the carrier, already severe, was compounded by the outbreak of serious fires which soon enveloped the entire ship. The situation soon became hopeless as the ship settled rapidly by the bow. Water quickly reached the flight deck and spilled through the open No. 1 elevator into the hanger. Thus stricken the Shokaku lost stability, turned over, and sank".
United States Strategic Bombing Survey (Pacific), "The Campaigns of the Pacific War", United States Government Printing Office, 1946.|
WDC 161517, "First Mobile Fleet Classified No. 1048 (5 September 1944), Detailed Battle Report of AGO Operations":
WDC 239992, "Impressions and Battle Lessons (Air) in the 'A' Operations":
"At 1120 the Shokaku was subjected to enemy submarine torpedo attacks (four hits) causing fire to break out and to sink at 1401."
"The Case of the Shokaku (carrier) -
Edo, Yuusuke. Higeki "Mariana oki no shichimenchouchi" (The Tragic "Marianas Turkeyshoot"), Kojinsha, 1992. pp. 252-261|
Translation paraphrased and abbreviated slightly:
struck on the starboard side forward, and also on the starboard side amidships. The first hit directly before the island, blasting fire and spray over the bridge and burning several aviators relaxing there. Since aircraft had just been landed, and were just then having been stored in the hangar, there was much fuel and materials about. Immediately a massive fire broke out, and an explosion blasted the hangar and raised all the elevators 90 centimeters.
As a result of the flooding from the torpedo holes, the Shokaku began to list quickly to starboard; to correct this, spaces were counterflooded on the port side----but this was done *too well*---with the result that Shokaku canted back over with a *reverse* heel to port! [Important detail. Ed.] and became waterlogged.
Meanwhile the hangar had become an inferno, for all power failed immediately, electric circuits went out, and extinguishing gear could not be used, no could anyone reach the hangar's mains. Therefore the crew desperately resorted to portable extinguishers and *bucket bridgades*---but this could not of course prevail against the fire, which also "dropped down like rain upon their heads" [av-gas burning and leaking from pipes? Ed.].
Shokaku became unnavigable, with the bow dipping, and stopped dead in the water. Many crew had died when they fell into the flames of hangar when the lifts jumped from the hits, and others had bodies "torn apart and scattered" by the explosions. Captain Matsubara soon realized that hope was lost, and gave the order for all hands to assemble and abandon the ship. Men went around calling for comrades, and several hundreds of men gathered on the flight deck for roll call even though the ocean had "already begun to swallow the front, having started to wash over the forecastle deck and was rising nearly to the level of the flight deck forward". Still the roll call continued for many sections, while others threw rafts and debris overboard and then lept after them.
Fires and explosions continued to increase, and then suddenly the ship upended, causing "sevaral hundreds" of men to slide from their feet on the flight deck aft all the way down to a fiery hell as they fell helplessly into the open fire-filled No.3 elevator; others tried to hang on for dear life. [Translator made grave expression as he read this, saying that the translation is describing *exactly* the effect of the movie Titanic which he had seen - just as horrible as the end. This made clear many otherwise vague words. Ed.].
At 2:10 the carrier finally "swung straight up" and with a "groaning roar" disappeared. Survivors remaining in the water began to sing with "blood tears" the Shokaku's ship song. The account gave the figures of 570 survivors, with 1,272 officersand men lost, and specifically called attention to the fact that the death toll was greater than carrier KAGA, which means the Japanese felt that flattop's casualty count keenly late in the war----a poignant detail.
Japan Self-Defense Agency. "Boeicho Kenshujo Senshishitsu (BKS), Vol. 12 - Marianas Campaign".|
"At 1120 Shokaku was torpedoed, caught fire, and sunk at 1410 in position 12°00' N, 137°46' E. Number of torpedo hits are not certain; survivors disagreed whether it was 3 or 4 hits."
Kojinsha. Maru Special Series "Imperial Japanese Navy, Vol. 3: Aircraft Carriers, Part I", 1994.|
"On 19 June 1944 attacked by submarine. 4 torpedoes hit, inducing fire from gasoline tank. Big fire resulted. Bombs exploded, and ship sank. 887 crew members and 376 of Air Group 601 were lost, for a total of 1,263 sharing the fate of the ship."
Cavalla, Report of War Patrol No. 1, No serial, 3 August 1944.|
CAVALLA's report reveals:
(using "I" time zone reference, per own current position)
1119 First torpedo of six fired hits Shokaku after 50 second run, followed by 2 and 3 at 8 second intervals, the next three miss.
1320 By now, only one destroyer (Urakaze?) is still working the Cavalla over of the three that initially pounced on her.
1330 Depth charging moves further away, but remains between Cavalla and scene of attack. About this time JP sound gear "began to report loud water noises in the direction of the attack."
1352 Cavalla commences planing up to periscope depth, with depth charges still heard intermittently, as well "could loud disturbance still be heard by JP in direction of attack."
1408-1411 "Four terrific explosions were heard in direction of attack. These were not depth charges or bombs, as their rumbling continued for many seconds."
1421 Cavalla reaches periscope depth:"Nothing in sight, visibility poor due to rain squalls all around."
1429 Cavalla secured from depth charge and silent running.
Kossler's Radio Report:
Secondary Sources Referenced
Samuel Eliot Morison. "History of United States Naval Operations in World War II, Volume VIII: New Guinea and the Marianas, March 1944 - August 1944", Little, Brown and Co., 1953.|
Norman Polmar. "Aircraft Carriers: A Graphic History of Carrier Aviation and its Influence on World Events", Doubleday, 1969.|
Note: Since Polmar collaborated with Minoru Genda on this book, this account may be reliable connection of the magazine explosion and the forward lift flooding being in that order, rather than just "guessed".
"The fumes created an explosive atmosphere which, shortly after 3.pm, caused the 25,675 ton Shokaku to blow apart. Her shattered hulk, enveloped in flames, began to sink by the bow. As her head went down water poured into the hangar deck through the forward elevator well and the ship quickly rolled over and sank. There were few survivors; 1,263 officers and enlisted men were lost-nine planes - five Judy, two Jill, and two Val bombers - went down with Shokaku."
Paul S. Dull, "A Battle History of the Imperial Japanese Navy (1941-1945),
U. S. Naval Institute Press, 1978.|
William T. Y'blood, "Red Sun Setting", U. S. Naval Institute Press, 1981.|
"The Shokaku was doomed. Her bow settled lower and lower in the water. Finally the water began to pour into the ship through her open forward elevator. Shortly after 1500 the fires cooked off a magazine and this explosion, intensified by volatile fumes, ripped the carrier apart. What was left of her turned over and sank at 12°00' N, 137°46' E. The Shokaku took with her 1,263 officers and men (out of a complement of about 2,000) and nine aircraft."