Japanese submarine I-402

I-402, was one of three completed Sen Toku I-400 class submarine aircraft carriers of the Imperial Japanese Navy. These submarines were the largest built prior to nuclear submarine development. Each were able to carry three Aichi M6A Seiran floatplanes.

Name: I-402
Builder: Sasebo Naval Yard, Japan
Laid down: October 1943
Commissioned: 24 July 1945[1]
Fate: Scuttled, 1 April 1946
General characteristics
Class and type: I-400-class submarine
  • Surfaced : 5,223 long tons (5,307 t)
  • Submerged : 6,560 long tons (6,670 t)
Length: 122 m (400 ft)
Beam: 12.0 m (39.4 ft)
Draft: 7.0 m (23.0 ft)
  • Surfaced : 4 × diesel engines, 7,700 hp (5,742 kW)
  • Submerged : Electric motors, 2,400 hp (1,790 kW)
  • Surfaced : 18.75 knots (34.73 km/h; 21.58 mph)
  • Submerged : 6.5 knots (12.0 km/h; 7.5 mph)
Range: 37,500 nmi (69,400 km) at 14 kn (26 km/h; 16 mph)
Test depth: 100 m (330 ft)
Complement: 144 officers and men
Aircraft carried: 3 Aichi M6A1 Seiran seaplanes
Aviation facilities: Watertight aircraft hangar

In 1942, 18 of these vessels were planned intended for attacks on the eastern seaboard of the United States and the eastern locks of the Panama Canal. However after increased shipping losses and the rising scarcity of alloys, only five were expected to be built. By 1944, only three had been completed (I-400 at Kure, I-401 and I-402 at Sasebo).

Entering service late in the war, I-402 never saw combat and was captured by the US at the end of the war.


I-402 was powered by four 3,000 horsepower diesel engines. The massive I-400 class submarine displaced 6,500 tons and had an overall length of 400 feet compared to the most numerous IJN submarine type, the B1 which only displaced 2,584 tons and had a length of 356 feet. The most notable characteristic of the I-402 was its ability to carry three Aichi M6A Seiran seaplane dive bombers. I-402 had a figure-eight hull shape for additional strength to handle the on-deck hangar for housing the three aircraft. The wings of the Seiran folded back, the horizontal stabilizers folded down, and the top of the vertical stabilizer folded over so the overall forward profile of the aircraft was within the diameter of its propeller. The planes were launched from a 120-foot catapult on the deck of the giant submarine. In addition, it had four anti-aircraft guns and a 14 cm 40 caliber deck gun as well as a suitable complement of twenty Type 95 torpedoes for commerce raids.

Post War Inspections

I-402 and her sister ships were captured by the United States Navy after the war. They were taken to Sasebo Bay for evaluation. While there, the Soviet Union planned to send inspectors to also study the unknown vessels. To keep the technology out of the hands of the Soviets, Operation Road's End was instituted. I-402 along with twenty other submarines were filled with C-2 explosive charges and scuttled off the Gotō Islands. In 2015, the precise location of the remains of 24 Japanese submarines, including I-402, was confirmed.[3]


  1. "World War II Database : Submarine I-402". ww2db.com. Retrieved 14 September 2010.
  2. Campbell, John Naval Weapons of World War Two ISBN 0-87021-459-4 p.191
  3. "24 scuttled Imperial Japanese Navy submarines found off Goto Islands". Japan Times. 8 August 2015. Retrieved 8 August 2015.

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