As commissioned on December 30th, 1944
Created for a covert strike against the critical Panama Canal, the I-400s could carry three Aichi M6A Seiran floatplanes to anywhere in the world, without refueling. They remain the largest diesel submarines ever constructed.
Details of I-400's early service are sparse, She participated in pilot training along with I-401, I-13, and I-14 between June 5th and 20th 1945, with pilots training for the attack on the Panama Canal.
When Okinawa fell, the plan of attack was changed, with the target now being Ulithi Atoll, where fifteen US carriers had assembled to stage raids on the Japanese Home Islands.
As captured on August 29th, 1945
I-400 was captured by USS Blue
, astonishing the destroyer's crew with her sheer size, being considerably larger than any of the American fleet boats. Her crew had ditched all the aircraft and torpedoes 7 days prior to her capture. At some point during her time as a prize boat, her nameplate was repainted with US style markings.
She was expended as a target on June 4th, 1946, sinking off the coast of Oahu.
As commissioned on January 8th, 1945
I-401, shown with one of her aircraft painted in fake US scheme, was commissioned too late in the war to accomplish her objectives, though made several attempts to launch. She had sailed for her first target by the time Emperor Hirohito's ceasefire broadcast was received on the 15th of August, 1945. She would hoist a black flag of surrender on the 26th, and all of her aircraft, weapons, codebooks, charts, and logs were destroyed. She would be captured by USS Segundo
on the 29th.
She was expended as a target on May 31st, 1946, sinking sinking off the coast of Kalaeloa, Hawai'i.
As commissioned on July 24th, 1945
I-402 was converted to a tanker submarine prior to commissioning and was never loaded with aircraft, she would see no action in the war.
She would be scuttled as a part of Operation Road's End on April 1st, 1946.
Displacement: 5,223 long tons surfaced, 6,560 submerged
Length: 122 m (400 ft)
Beam: 12 m (39.3 ft)
Draft: 7 m (22.9 ft)
Propulsion: Four diesel engines generating 7,700 shp, two electric motors generating 2,400 shp
Range: 37,500 nm at 14 kts surfaced, 30,000 nm at 16 kts. 60 nm at 3 kts submarged.
Test depth: 100 m (330 ft)
Complement: 21 officers, 170 enlisted men
Armament: 8 × 533 mm (21 in) forward torpedo tubes with 20 × Type 95 torpedoes, 1 × 14 cm/40 11th Year Type naval gun, 3 × 35 mm (1.4 in) 3-barrel machine gun, 1 × Type 96 25 mm (0.98 in) machine gun
Aircraft: Three Aichi M6A Seiran special attack aircraft
"This is really quite bad." - Unknown sailor on board the battleship Ustoppelig
, moments before magazine detonation