Midget Submarines at Pearl Harbor, Hawaii

© 2006-2017 Bob Hackett and Sander Kingsepp

Revision 4

10 October 1940:
The first batch of ten Type A midget submarines (Nos. 3 to 12) is ordered from the Karasu-Kojima Torpedo Factory.

15 November 1940:
The midget submarine is accepted into IJN service as "Type A improved ASW target" (Ko-Hyoteki). That same day, a group of 13 officers and petty officers arrives aboard Captain (Vice Admiral, posthumously) Harada Kaku's (41)(former CO of HOSHO) CHIYODA for classroom training in midget submarines, directed by Cdr (Rear Admiral, posthumously) Kato Ryonosuke (48).


January -March 1941:
The first group undergoes sea training and further instruction.

April 1941:
Training of the first group is completed. A second group of ten officers and 12 petty officers and ratings arrives and begins training. Sea training is conducted aboard CHIYODA and Captain (later Rear Admiral) Komazawa Katsumi's (42)(former CO of CHOGEI) newly commissioned seaplane/submarine tender NISSHIN. Only two officers of all the midget submariners are volunteers; the rest are routinely assigned the duty.

May 1941:
Mitsukue Bay (Ehime Prefecture), off Shikoku. The second group of trainees simulates attacks on anchored vessels. Tug KURE MARU serves as temporary base.

June-July 1941:
Seaplane tender CHIYODA undergoes a modification to her stern to form a ramp to enable her to launch midget submarines.

18 August 1941:
The second group conducts its final exercise, using CHIYODA as the target. During a subsequent conference, some crewmembers suggest use of the new weapon to penetrate enemy naval bases to attack capital ships. They also suggest the use of "mother" submarines as midget carriers to overcome the midget submarines' short range problem. Soon thereafter, training of the second group is completed.

Early September 1941:
Naval General Staff (NGS) liaison officer Cdr (Rear Admiral, posthumously) Ariizumi Tatsunosuke (51) inspects CHIYODA. Captain Harada informs him of the harbor-penetrating concept and asks that Ariizumi forward the idea to the NGS. Harada, Lt Iwasa Naoji (65) and Lt(j.g.) Matsuo Keiu (66) compile several studies about attacks on naval bases at Pearl Harbor, San Francisco, Hong-Kong, Singapore and Sydney.

Late September 1941
Aki Nada, Inland Sea. To verify the feasibility of penetrating an enemy harbor with midget submarines, Captain Harada conducts a series of night exercises in Hirajo Bay, Shikoku. The midget submariners operating from Captain (later Rear Admiral) Furukawa Tamotsu's (43)(former CO of KAMOI) seaplane/submarine tender CHITOSE practice attacking a defended harbor that, unknown to them, resembles Pearl Harbor and returning to the unlit CHITOSE at night.

4 October 1941:
A planning conference is held aboard the Combined Fleet's temporary flagship battleship MUTSU, concerning the details of the forthcoming attack on Pearl Harbor. Captain Harada appeals to C-in-C Admiral (Fleet Admiral, posthumously) Yamamoto Isoroku (former CO of AKAGI) to use the midget submarines in parallel with the air attack. Admiral Yamamoto suggests Harada reconsider his idea and report back to him the next day.

5 October 1941:
Captain Harada, accompanied by Lt Iwasa and Lt(j.g.) Matsuo, returns to MUTSU. The junior submariners plea directly to Admiral Yamamoto to permit the use of midget submarines in the Hawaii Operation. Most air staff officers vehemently oppose the idea.

11-13 October 1941:
Hashirajima. At another planning conference aboard the Combined Fleet's flagship battleship NAGATO, Admiral Yamamoto approves the use of midget submarines in the forthcoming Hawaii Operation. Several months later, the midget submarine part of the Pearl Harbor attack is designated as "Shinki"(Divine Turtle") Operation No. 1.

19 October 1941:
Headquarters, Sixth Fleet (Submarines) issues an order to convert five midget submarines and five Type C-1 mother submarines for the Hawaii Operation. To upgrade the harbor penetrating capabilities of the midget submarines, they are fitted with a pneumatically operated steering system. Twenty-five batteries from the forward battery room are landed and replaced by four additional air bottles for the steering system. The range at low speed is marginally increased, but the maximum speed drops to 16 knots. A scuttling charge is fitted into the aft battery room. All midget submarines are fitted with net guard/cutters, jumping wires and propeller guards. Running lights are blanked off. A built-in telephone is fitted to communicate with the mother submarine. All work is finished by 10 November.

22 October 1941:
Yokohama. The Nippon Yusen Kaisha (NYK) liner TAIYO MARU departs for Hawaii. Aboard disguised as crew members are three IJN officers: Cdr (later Rear Admiral) Maejima Toshihide (48), LtCdr Suzuki Suguru (55) and midget submarine pilot Lt Matsuo Keiu. TAIYO MARU plies the North Pacific route that will be followed by the Kido Butai carrier striking force in the Hawaii Operation. [1]

1 November 1941:
Oahu, Hawaii. At 0830, TAIYO MARU arrives at Honolulu. Lt Matsuo's mission is to reconnoiter the harbor entrance to Pearl Harbor's naval base.

5 November 1941:
The three IJN officers depart for Japan aboard TAIYO MARU.

14 November 1941: - The Hawaii Operation:
Headquarters, Kure Naval District. Vice Admiral Shimizu Mitsumi (36), C-in-C, Sixth Fleet (Submarines) and his chief of staff, Captain Mito Hisashi (42) lead a staff conference. Fleet submarines I-16, I-18, I-20, I-24 and I-22 (F) are assigned to Captain (later Rear Admiral) Sasaki Hankyu's () Special Attack Unit.

Cdr Arima Takayasu (52), the Combined Fleet's senior torpedo staff officer, briefs Captain Sasaki and the five midget submarine officers of the Special Attack Unit on the Hawaii Operation. According to the battle plan, the midget submarines will be employed only in case the major part of the U.S. Pacific Fleet is stationed at Pearl Harbor anchorage. The midget submarines have to attack in the lull between the two air strikes and arrive at the rendezvous point 7 nms ESE of Lanai Island on 8 December.

17 November 1941:
Yokohama. TAIYO MARU arrives. Cdr Maejima and Cdr Suzuki provide an intelligence briefing to the top officers of the NGS's headquarters. Afterwards, Cdr Maejima and Lt Matsuo rush to the Kure Navy Club and arrive just in time to brief the midget submarine crews' officers on Pearl Harbor's defenses.

18 November 1941:
Early in the morning, the Special Attack Unit departs Kure for the Kamegakubi Naval Proving Ground. At Kamegakubi each of the unit's submarines embarks a top-secret two-man Type A midget submarine. In the evening, the last conference is held, led by Cdr Ariizumi.

19 November 1941:
At 0215, all five of the Special Attack Unit's submarines depart for the Hawaiian Islands. Lt Matsuo, whose intelligence duties precluded him being designated a midget submarine CO for the operation, is aboard I-22 as XO of the Special Attack Unit. While at sea, the enlisted midget submariners are briefed on the Hawaii Operation. The mother submarines use a direct route, but pass Wake and Midway islands at 600-mile distance to avoid detection by aircraft.

2 December 1941:
The coded signal "Niitakayama nobore (Climb Mt. Niitaka) 1208" is received from the Combined Fleet. It signifies that hostilities will commence on 8 December (Japan time).

7 December 1941 (Local): The Attack on Pearl Harbor:
Submarines I-68 and I-69 are ordered to lay off the entrance to Pearl Harbor to rescue midget submarine crews.

At 0042, I-16 launches Lt(j.g.) Yokoyama Masaji (67) and PO2C Ueda Sadamu's midget submarine HA-16 about seven miles SSW of the harbor's entrance. M-16 is the first of five midget submarines released by the Special Attack Unit.

At 0116, I-22 launches Lt Iwasa Naoji (one of the two volunteers) and PO1C Sasaki Naokichi's HA-15 about nine miles from the harbor's entrance.

At 0215, I-18 launches Lt(j.g.) Furuno Shigemi and PO1C Yokoyama Shigenori's HA-17 from about 13 miles from the harbor's entrance.

At 0257, I-20 launches Ensign Hiroo Akira and PO2C Katayama Yoshio's HA-18, 5.3 miles from the harbor's entrance.

At 0333, I-24 launches Ensign Sakamaki Kazuo and PO2C Inagaki Kiyoshi's HA-19, 10.5 miles WSW of the harbor's entrance. HA-19 begins to broach, but Inagaki manages to correct the trim successfully.

Pearl Harbor Midget Submariners [2]
(Naval Historical Center)

At 0408, LT W. W. Outerbridge's old USS WARD (DD-139) begins a search for a suspected submarine reported by minesweeper CONDOR (AMC-14), but finds nothing. At 0630, as Training Squadron 8's flagship 8 USS ANTARES (AKS-3) approaches Pearl's outer gate with a target raft in tow, WARD's lookouts spot a small conning tower. A patrolling PBY "Catalina" flying-boat 14-P-1, flown by Ensign William P. Tanner of Patrol Squadron VP-14, drops smoke markers on the contact.

At 0645, WARD opens fire at 100 yards. Her first round - the first shot fired in WWII by American Forces - misses. She closes to point blank range (50 yards) and fires a 4-inch shell, hitting the midget submarine's conning tower. WARD overruns her target and the midget submarine wallows in her wake. Outerbridge orders four depth charges dropped. At 0651, he signals 14th Naval District Headquarters:


The PBY drops more depth bombs. A midget submarine, thought by some researchers to be Hiroo and Katayama's HA-18, is sunk.

At 0700, Sakamaki’s midget submarine HA-19 makes the harbor entrance, but cannot enter the harbor before the air strike commences.

At 0755, the Striking Force's first wave of 189 aircraft attack the Naval Base at Pearl Harbor and other military installations on Oahu, Territory of Hawaii.

About 0800, Sakamaki surfaces, but runs aground on a reef. HA-19's gyro compass malfunctions and Sakamaki has to expose his periscope frequently for navigation. At 0817, HA-19 is spotted by USS HELM (DD-388) that opens fire on the midget submarine and misses, but HA-19's lower torpedo tube, net guard/cutter and vertical rudder are damaged by the collision with the reef. Inagaki shifts lead ballast bars aft of batteries while Sakamaki runs full power astern. HA-19 slips off the reef. Later, the midget submarine's batteries exude chlorine gas that knocks the crew unconscious. When Sakamaki comes to, he sees smoke from ships burning in the harbor.

Battleship Row under Air Attack
(U. S. Navy)

During the air attacks, the Striking Force sinks battleships ARIZONA (BB-39), OKLAHOMA (BB-37) and CALIFORNIA (BB-44) and damages NEVADA (BB-36), PENNSLYVANIA (BB-38), TENNESSEE (BB-43), MARYLAND (BB-46), WEST VIRGINIA (BB-49) and other smaller ships.

HA-19 runs aground again. Sakamaki and Inagaki shift ballast and free the midget submarine, but it will not answer the helm. Drifting, HA-19 is depth charged several times. Sakamaki tries to beach her, but runs aground again. He lights the fuse of the midget submarine's self-destruct charge and leaps into the surf where he is battered unconscious again and washes ashore on Waimanalo Beach near Bellow's Field. The scuttling charge does not explode. Both of HA-19's torpedoes are found intact aboard the midget submarine. [3]

Location where Sakamaki and Inagaki's HA-19 was found
(Scanned from H.P. Willmott's "Pearl Harbor")

At 0830, LtCdr William P. Buford's USS MONAGHAN (DD-354) is attempting to sortie from Pearl Harbor via the North Channel to evade the on-going air raid when nearby destroyer/minesweeper USS ZANE (DMS-14) reports "sighted enemy submarine 200 yards astern of MEDUSA." Minelayer BREESE (DM-18) spots the midget submarine next, followed by seaplane tender CURTISS (AV-4) that opens fire.

At 0837, MONAGHAN spots the submarine's periscope and part of its conning tower about 1,200 yards off her starboard bow. LtCdr Buford orders flank speed and prepares to ram. In the meantime, repair ship USS MEDUSA (AR-1) and tender TANGIER (AV-8) open fire on the midget submarine.

The submarine fires a torpedo at CURTISS, but broaches and is hit by a 5-inch shell fire from the tender that probably decapitates her skipper. The midget submarine is also raked by .50 cal. machine-gun fire. Her torpedo misses CURTISS and hits a dock. MONAGHAN bores in on the submarine. The midget turns into the destroyer and fires its last torpedo. It just misses to starboard and explodes against the shore of Ford Island. MONAGHAN rams the midget submarine and pushes her down to the bed of the 30-foot deep harbor. The destroyer then drops two depth charges that blow the midget submarine to the surface. The midget submarine sinks NW of Ford Island.

A midget submarine, possibly Furuno and Yokoyama's HA-17, is depth-charged and sinks in the Keehi Lagoon just off Pearl Harbor.

About 0840, a second wave of 171 aircraft attacks the Naval Base By 0945, they retire towards their carriers.

Captain George A. Rood's ST. LOUIS (CL-49), steaming at 25 knots, is the first major unit to reach open water. At 1004, as she stands by the first entrance buoy to the South Channel, a midget submarine fires two torpedoes from 2000 yards on her starboard beam. Both miss, but only because they ground on a reef to the west of the dredged channel.

At 2241, I-16 is patrolling west of Lanai, Hawaii when she receives a "Se, se, se!” (short for seiko, or success, success, success) message about the successful air attack. Some researchers think it may have come from Lt Yokoyama's midget HA-16, but it may well have come from any of the midget submarines because the reception was very poor.

8 December 1941:
At 0051, I-16 receives another message thought by some to be from Yokoyama that says "unable to navigate." All five of the Special Attack Unit's midget submarines fail to return to their "mother" submarines.

That same day, Ensign Sakamaki is taken prisoner - the first POW taken by the United States in the Second World War.

Sakamaki and Inagaki's Beached Type A Midget Submarine HA-19
(U. S. Navy)

December 1941:
A midget submarine, identified by some researchers as Lt Iwasa's HA-15, is raised about two weeks after the attack. A No. 1 dress blues sleeve with rank insignia of a full Lieutenant was found floating in the harbor. It may have belonged to Iwasa or one of the downed Japanese pilots. Iwasa was the only officer of that rank in the midget submarine attack force. The sleeve is returned to the Japan by the U.S. Navy in March 1947 and has been on display at the Yasukuni Shrine, Tokyo since 1972. Some Japanese researchers theorize that HA-15 was the midget submarine that tried to torpedo CURTISS and was rammed and sunk by MONAGHAN, however, this identification is speculative. The hulk of the raised midget was salvaged, but was in such a bad shape that no one entered it. Her screws and net guard/cutters were salvaged and used in the reconstruction of HA-19. The remainder of the wreck was dumped during the S-1 submarine dock reconstuction at Ford Island. It was rediscovered in 1952, but reburied at the same place because chlorine gas had eaten away all its contents. The remains of the crew are still inside.

6 March 1942:
The crews of all the Pearl Harbor midget submarines, except PoW Sakamaki, are posthumously promoted two ranks.

21 May 1944: The Second Pearl Harbor Disaster:
West Loch anchorage, Pearl Harbor. At 1508, an explosion of Landing Ship Tank LST-353 wracks the amphibious staging area sinking six LSTs readying to sail to the Marianas Islands for the invasion on Saipan, codenamed "Operation Forager."

West Loch Anchorage Disaster

The blast appears to have originated near the bow of LST-963, where Army troops were unloading heavy mortar ammunition. Fragments shower the clustered LSTs, igniting gasoline drums lined up on them. Each LST carries trucks, jeeps, and weapon carriers on their main decks, all of which are loaded with ammunition and gas. Each vessel also carries 80 to 100 drums of high-octane fuel on its forecastle. Six thousand cubic feet of ammunition are stowed on the deck with field guns and amphibious craft known as DUKWs. Explosions begin to rip the invasion fleet apart. In all, six LSTs are sunk and several severely damaged. 163 men are killed and 396 wounded. The disaster becomes one of the Navy's best-kept wartime secrets.

The United States LST Association's website gives more details on the West Loch disaster at:

13 June 1960:
A midget submarine is discovered in the Keehi Lagoon in only 75 feet of water.

6 July 1960:
The Keehi Lagoon midget submarine is raised by the submarine rescue ship USS CURRENT (ARS-22). No human remains are found aboard. The conning tower hatch is open. Inside the midget submarine the remains of a flightsuit, one flying boot, a single glove, rubber-soled sandal, an empty bottle of sake, several wrenches and spanners are found. Based on this evidence, some researchers identify that midget as Lt(j.g.) Furuno's HA-17.

The forward section is found to contain both torpedoes intact. The section is unbolted and it and the torpedoes therein are disposed of at sea. Much later, the entrance to Keehi Lagoon is covered by the extension of Honolulu International Airport's runway. At the request of the Japanese Government, the remainder of the midget submarine is returned to Japan. A new forward section is fabricated and the midget submarine is now at the Naval Tactical School No. 1 at Etajima, Hiroshima, another of the four Type A midget submarines on display around the world.

Pearl Harbor Type A at Etajima

August 1966:
Suga Park, Mitsukue Bay, Ehime Prefecture. The pilots of the midget submarines that attacked Pearl Harbor trained at the submarine base at Mitsukue Bay which has geographical characteristics similar to Pearl Harbor. Seto Town erects a monument to honor the nine men who died in the attack on Pearl Harbor.

Nine War Gods Monument at Suga Park

27 July 1992:
A team from the University of Hawaii’s Undersea Research Laboratory (HURL), in the deep-submersible vehicle PISCES V locates the aft section of a Type A midget submarine 1200 feet down in the Defensive Sea Area several miles off Pearl. Postwar, this area became a dumping ground for hundreds of items of obsolete or discarded war materials, such as landing craft, tanks, old aircraft, trucks, barges, small ships, fuel tanks etc. The aft section is located in this field with other debris. Unfortunately, PISCES V's tracking system is malfunctioning and cannot provide reliable coordinates to the surface. As a result, the location of the aft section of this Type A is temporarily "lost". [4]

5 September 2000:
PISCES V locates the mid-section of a Type A midget submarine at 1200 feet in the Defensive Area. The mid-section is missing about 15 feet aft of the conning tower, possibly caused by the submarine's scuttling charges. A survey of this section indicates that it most probably was dumped here. [4]

9 November 2000:
Famed Wood's Hole Oceanographer and undersea explorer Bob Ballard's deep-water remote-operated imaging vehicle ARGUS lights up the remains of a Type A midget submarine in the Defensive Area dumping ground. Only its mid-section and sail remains. This mid-section is the same one HURL found two months earlier. It is theorized that this midget submarine had been captured in another campaign, possibly Guam, studied by intelligence experts at Pearl, then dumped. [4]

29 August 2001:
PISCES IV is en route to the mid section discovered the previous fall when the dive team locates the bow-section of a Type A midget submarine at 1200 feet. The bow is fitted with an early "figure 8" net guard/cutter. The torpedo tubes are empty. A hole has been punched in forward part of this bow section to allow a hawser to be attached to drag and dump the section into the Defensive Area. After filming these two sections the team continues exploring and "rediscovers" the tail section found nine years earlier. [4]

Forward Bow and Mid-sections of Type A
(Hawaii Undersea Research Laboratory)

28 August 2002:
PISCES IV and PISCES V discover a midget submarine in 1,312 feet (400 m) of water five miles off Pearl Harbor. There is a 4-inch hole in the conning tower and both of her torpedoes are still aboard. This seems to conclusively prove that this midget submarine is one sunk by USS WARD and Ens Tanner's PBY. It is thought by some researchers to be Hiroo and Katayama's HA-18, however, this identification is speculative.

Pearl Harbor Type A found by HURL showing hole in conning tower
(Hawaii Undersea Research Laboratory)

Authors' Notes:
In reality, the HA-type numeration was not used by the IJN during the Pacific War. HA-numbers are here adopted for convenience. The numbers for all the Pearl Harbor midget submarines, except Sakamaki and Inagaki's HA-19, originate from the work of the Japanese historian Katsume Junya (2011). Attribution by researchers of actions to specific midget submarines, other than HA-19, is mostly speculative.

[1] Lt Matsuo is later KIA in the attack on Sydney, Australia.

[2] The nine submariners lost at Pearl are from the left: P02C Katayama Yoshio of I-20, PO1C Sasaki Naokichi of I-22, PO1C Yokoyama Shigenori of I-18, Ens Yokoyama Masaji of I-16, Lt Iwasa Naoji of I-22, Lt(j.g.) Furuno Shigemi of I-18, Ens Hiroo Akira of I-20, P02C Ueda Sadamu of I-16 and P02C Inagaki Kiyoshi of I-24.

Ensign Sakamaki Kazuo of I-24's HA-19, taken prisoner, is not shown in this Japanese painting. The IJN public affairs department circulated a rumor to explain the missing crewmember to the effect that Lt Iwasa had led his craft single-handedly. The IJN credited the midget submarines with sinking USS ARIZONA 13 hours after the air attack.

[3] Since 1991, Sakamaki and Inagaki's midget submarine HA-19 has been displayed at the Fleet Admiral Chester A. Nimitz "National Museum of the Pacific War" in Fredericksburg, Texas, one of four such Type A midget submarines on display around the world.

Sakamaki's HA-19 at the National Museum of the Pacific War


[4] All three sections discussed and pictured above when discovered by HURL in 1992, 2000 and 2001 were found to have been disconnected at the joining sections, had rigging cables attached and had been scuttled. An approximately 15-foot piece of this midget submarine’s aft mid-section, as shown on the drawing below, is still missing. This piece is from the jagged end where a scuttling charge blew the stern off, to where the bolts of the intact part of the stern section were later cut off with a torch or saw.

Missing M-16?

The origin of the three sections of the midget submarine is unknown, but Terry Kerby, HURL's Director of Operations, has developed a theory that makes sense. His theory centers on "The Second Pearl Harbor Disaster" discussed above.

Kerby believes the three pieces were discovered during clean up of West Loch. The civilian salvers probably lifted the two main pieces of the hull onto a crane barge and disassembled it at its flange joints to make it easier for disposal. Later, the three pieces were dumped in the Defensive Sea Area, along with other debris from West Loch.

HURL's investgators verified that the submarine pieces had been disassembled and rigged with cables for easier handling. The West Loch Disaster was placed under a veil of secrecy, so there was no record of the salvage and disposal.

As noted above, the torpedo tubes in the bow-section of the Type A midget submarine found on 29 August 2001 were empty. HURL's theory is that this midget fired its torpedoes at Captain (Rear Admiral-Ret) George A. Rood's USS ST. LOUIS (CA-49) as she exited South Channel out of Pearl Harbor at 22 knots. Both torpedoes missed and exploded on the reef.

Finally, Rear Admiral Ueda Kazuo (JMSDF-Ret)(a midget submarine commander and ex-staff member of the Japanese Midget Submarine Association) confirmed that only the Pearl Harbor midgets had the "figure 8" net guard/cutter over the torpedo tubes. Thus, there is strong evidence that the three pieces discovered in the Defensive Sea Area comprise the missing fifth midget submarine. It is thought by some researchers to be Yokoyama and Ueda's HA-16, however, this identification is also speculative.

Many thanks go to Steven L. Price of the Hawaii Undersea Research Laboratory for assistance with this revision.

For further information/speculation about the missing fifth midget submarine and the three-piece midget submarine, see: I-16tou.

-Bob Hackett and Sander Kingsepp

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