Ulithi Atoll, Caroline Islands, Western Pacific January 9, 1945

Toward the end of 1943, the Japanese high command in Tokyo recog­nized the unfavor­able pro­gress of the war that shrank their nation’s watery outer defense peri­meter closer and closer to the four Home Islands them­selves as the Allies seized one Pacific island after another. Seemingly over­night Allied air­fields and supply bases appeared where none had existed before. One famously des­perate reaction by the enemy was to recruit one-way pilots of air­craft (Kami­kaze), human-guided bombs (Ohka), and sui­cide boats (Shinyo) and one-man mini-submarines (Kaiten).

The seeds of the Japanese Navy building a fleet of no-return mini-sub­marines, or Kaiten (often trans­lated “Turn the Heaven” or “Turn of Heaven’s Will”), were sown in mid-1944. The very first Kai­ten, a Type 1, was not much more than a Japa­nese Type 93 (“Long Lance”) tor­pe­do war­head and engine com­part­ment attached to a cylin­der that would become the pilot’s com­part­ment and Kai­ten’s after­body. In all there were 7 types (or classes) of Kai­tens, but only the Type 1 saw oper­a­tional deploy­ment. The Type 10, dif­fer­ent from all other Kai­tens, was based on the sub­marine-launched Type 92 tor­pe­do and carried a war­head one‑fifth the size of a Type 1. Just one proto­type and 2 or 6 Type 10s were built. As for the Type 1, approx­i­mately 330 were built, of which more than 100 were sent on one‑way missions.

Type 1 vessels weighed in at 8.3 long (Imperial) tons/­8.4 metric tons, had a length of 48 ft 5 in/­14.75 m, and a dia­meter of 3 ft 3 in/­1 m. Type 1s carried a 3,420 lb/­1,550 kg war­head. Kai­tens were launched from the decks of sub­marines (21), destroyers (14), and one light cruiser. The first deploy­ment of Type 1 Kai­tens—the Kikusui group, so named for kiku (chry­san­the­mum) and sui (water)—was launched by mother sub­marines I‑36 and I‑47 on Novem­ber 20, 1944, out­side Ulithi’s large, 212sq. mile/­549sq. km lagoon. Up until early 1945 Ulithi Atoll was the U.S. Navy’s largest for­ward supply, replen­ish­ment, and repair base in World War II. One of I‑47’s Kai­tens in­side the Ulithi lagoon dis­patched the U.S. fleet oiler Missis­sinewa and 63 men to a watery grave (see photo essay). All 8 pilots and Kai­tens were lost in this ini­tial deploy­ment of Japan’s newest Kamikaze weapon.

The second deployment of Kaitens, known as the Kongo (“Steel”) group, occurred on this date, Janu­ary 9, 1945. Mother sub 1‑36 made a repeat visit to Ulithi on Janu­ary 12, her Kai­tens sinking an infan­try landing craft (3 deaths) and damaging a destroyer (8 casual­ties). 1‑36’s Novem­ber 1944 com­pat­riot I‑47 launched 4 Kai­tens off Hol­landia on the north coast of New Guinea (part of the then Dutch East Indies) and missed scoring a second sinking by only damaging a 7,247ton Liberty cargo ship.

Four more mem­bers of the Kongo group fared poorly. Kai­ten carrier I‑48 took I‑47’s former place at Ulithi but went down with all 122 hands when sunk by a U.S. Navy destroyer. Mother­ship I‑53 managed to launch 4 Kai­tens off Kossol Roads, a large reef-enclosed anchor­age in the Palau island chain that was used suc­ces­sively by Japan and the U.S. as a fleet anchor­age. None of the four reached its target; indeed, two failed to travel any dis­tance at all. Mother­ship I‑56 embar­rassed her­self and Japa­nese Emperor Hiro­hito (post­humously referred to as Emperor Shōwa) by failing to reach her tar­get, See­adler Har­bor on Manus Island in north­ern Papua New Guinea, returning home with her full com­ple­ment of Kai­tens. Finally, mother­ship I‑58 launched all 4 Kai­tens off Apra Harbor, a deep-water U.S. naval base on Guam, only to have one Kai­ten explode immed­i­ately after launch and the other three dis­appear in pillars of smoke off in the distance along their general bearing.

The Kaiten Human Torpedo—Japan’s Newest Kamikaze Weapon

Kaiten human-piloted torpedo Type 1

Above: Of the 7 Kaiten type classes, only the Type 1 was used oper­a­tion­ally. The Type 1 had a maxi­mum range of 42 nau­ti­cal miles/­78 km and sped through the water at speeds between 5.1 kn/­9.5 km/h (mini­mum) and 30 kn/­56 km/h (maxi­mum). Kai­tens turned out to be a pipe dream of Japa­nese Navy brass as a way of staving off the nation’s inev­ita­ble defeat. The human-guided torpe­does sent just 3 U.S. ships to the ocean floor between Novem­ber 20, 1944, and mid-August 1945, when Japan’s emperor capit­u­lated to the Allied victors. During the same period at least 106 Kai­ten pilots died in their Kai­ten coffins attacking U.S. ships and a further 15 in training mis­haps. Eight hun­dred sailors perished when their mother subs were sunk. For every 4 Japa­nese who died in Kaitens or in mother subs, 1 American died.

Kaiten human-piloted torpedo: Final moments of the auxiliary fleet oiler USS Mississinewa, Ulithi, November 20 1944Kaiten human-piloted torpedo: Type 1 test, Kure, Feb. 18, 1945

Left: The U.S. auxiliary fleet oiler Mississinewa, at anchor in the Ulithi lagoon, was sunk on the morn­ing of Novem­ber 20, 1944, by a Kaiten launched from I‑47 just out­side the lagoon. Ulithi coral reef lagoon in the West­ern Pacific Caro­line archi­pelago could accom­mo­date over 700 ships with plenty of room for refueling, repair, main­te­nance, and storage oper­a­tions. The Kai­ten attack was the first suc­cess­ful attack by Japan’s kami­kaze mini-subs. The Mississinewa’s cargo tanks were filled nearly to the brim with 404,000 U.S. gallons of avi­a­tion gas, 9,000 barrels of diesel fuel, and 90,000 barrels of fuel oil. The explo­sion of the Kai­ten’s war­head in the front star­board bow area rocked the oiler. A second explo­sion occurred when an avi­a­tion gas cargo tank ignited. Fires reached the after maga­zine and caused yet an­other explo­sion. Flames towered 100 ft/­30 m over the wounded ship. A little over 4 hours later the oiler slowly rolled over on its port side and dis­appeared beneath the oily sur­face, taking with it 63 hands out of 299 officers and enlisted men.

Right: Most of the Type 1 Kaitens were sent into com­bat by 21 sub­marines. A smaller num­ber of launch ves­sels (14) were destroyers and a single light cruiser. Destroyers and the light cruiser Kita­kami could accom­mo­date 8 Kaitens, 4 on the port side and 4 on the star­board. Sub­marines accom­mo­dated 4 Kai­tens. The Kai­tens were tested at Kure Naval Arsenal near Hiro­shima. The naval arsenal lay on the Seto Inland Sea as did the Sasebo Naval Arsenal. A series of emer­gency repairs owing to a British tor­pedo attack in late Janu­ary 1944 forced the Kita­kami to Sasebo Naval Arsenal later in August for repairs and modi­fi­ca­tion into a human tor­pedo car­rier. The refit was com­pleted 5 months later, after which the cruiser was assigned directly to the Imperial Navy Com­bined Fleet, home port Kure, to train Kai­ten pilots in the Seto Inland Sea as shown in this photo­graph. This late in the war fuel short­ages limited the cruiser’s training sorties.

Kaiten human-piloted torpedo traineeKaiten human-piloted torpedo: Kaiten-carrier I-47, November 1944

Left: A volunteer Kaiten pilot in training maneu­vers wears a white silk hachi­maki around his head. The great major­ity of Kai­tens were Type 1 Kai­tens and were based on Japan’s suc­cess­ful Type 93 “Long Lance” tor­pe­do, which burned eth­a­nol or meth­a­nol. The photo­graph above may depict this samu­rai war­rior wrestling with a Type 10 Kai­ten, which was built around a Type 92 elec­tric tor­pe­do. Only 1 proto­type and 2 or 6 were ever pro­duced. The Type 10 Kai­ten was tiny compared to Type 1 Kai­tens. Entered through an upper, not lower, hatch, the Type 10 Kai­ten at 2.3 ft/­0.7 m in dia­meter—impos­sibly cramped, stifling, and uncom­fort­able for the pilot and plagued by sea­water leaks into the bat­tery com­part­ments and pilot’s com­part­ment—carried a war­head just a fifth the size of a Type 1 Kai­ten. Never­the­less, the Japa­nese Naval com­mand ordered con­struc­tion of more than 500 Type 10s.

Right: Commissioned in July 1944, I‑47 operated as a Kaiten human-piloted tor­pedo car­rier during the final year of the Pacific War. I‑47 was one of two mother sub­marines that com­posed two-thirds of the Kikusui-tai Kaiten (“Floating Chry­san­the­mum”) trio assigned to mount the first Kai­ten oper­a­tion of the war—in the case of I‑47 and I‑36 on the U.S. anchor­age at Ulithi Atoll in the Caro­line Islands. I‑37, the third mem­ber of the Kaiten oper­a­tion, came to grief off the Philip­pine island of Leyte, its objec­tive, on Novem­ber 19, 1944. Three days earlier, on Novem­ber 16, Japa­nese recon­nais­sance air­craft had made a high-alti­tude flight over Ulithi Atoll and sighted 4 fleet air­craft car­riers and 3 battle­ships as well as many crui­sers and destroyers in the north-central part of the lagoon and trans­ports, oilers, and other ships in the south-central part. In fact over 200 ships were at anchor in the lagoon that week. On Novem­ber 20, 1944, between 3:28 and 3:42 a.m., I‑47 launched its Type 1 Kai­tens. I‑36 managed to launch a single Kai­ten, which a U.S. war­ship sank. At 5:47 a.m. one of I‑47’s Kai­tens rammed the hull of U.S. Navy fleet oiler Missis­sinewa, which caught fire, cap­sized, and sank at 9:28. After exam­ining after-action reports and post-attack recon­nais­sance photo­graphs, the Japa­nese mis­takenly cred­ited the Ulithi attack with sinking 3 air­craft car­riers and 2 battle­ships when only a fleet oiler was sunk. Radio Tokyo declared the Ulithi attack a rip-roaring success.

Kaiten: Japan’s Crewed Attack Torpedo and Suicide Craft, 1944–1945