Japanese submarine I-400

Japanese submarine I-400 was a large Imperial Japanese Navy submarine, designed to carry Aichi M6A Seiran floatplane bombers, and served during World War II. The I-400 was constructed at the Kure Naval Arsenal and launched on January 18, 1944, with Captain Tatsunosuke Ariizumi as its first commander, who had previously served on the Japanese submarine I-8. The development of the I-400 was influenced by the Japanese aircraft carrier Akagi and the German U-boat U-47, which had been studied by the Imperial Japanese Navy.

● Design and Construction

The design of the I-400 was based on the earlier Japanese submarine I-13 and Japanese submarine I-14, with a larger hull and more powerful diesel engines, similar to those used on the German battleship Bismarck. The I-400 had a length of 122 meters, a beam of 12 meters, and a draft of 7 meters, making it one of the largest submarines in the world at the time, comparable to the United States Navy's USS Triton (SSRN-586). The construction of the I-400 was supervised by Rear Admiral Umezu Yoshijiro, who had previously overseen the construction of the Japanese battleship Yamato and the Japanese aircraft carrier Shinano. The I-400 was equipped with advanced sonar and radar systems, including the Type 22 radar and the Type 3 sonar, which were also used on the Japanese destroyer Akizuki.

● Operational History

The I-400 began its operational career in 1945, with a mission to attack the Panama Canal, which was a crucial strategic location for the United States Navy and the British Royal Navy. The I-400 was commanded by Captain Ariizumi Tatsunosuke, who had previously served on the Japanese submarine I-8 and had participated in the Attack on Pearl Harbor. The I-400 sailed from Nanao Bay on July 23, 1945, and traveled to the Marshall Islands, where it met with the Japanese submarine I-401 and the Japanese submarine I-14. The I-400 was also supported by the Japanese submarine tender Tsukushi, which provided logistical support and maintenance services. However, the mission was cancelled due to the Allied invasion of Japan and the Soviet invasion of Manchuria, which led to the Japanese surrender.

● Characteristics

The I-400 had a displacement of 6,500 tons, making it one of the largest submarines in the world at the time, comparable to the Soviet submarine K-222. The I-400 was powered by four diesel engines, which produced 7,700 horsepower, similar to the German battleship Tirpitz. The I-400 had a range of 37,500 nautical miles, making it capable of traveling from Japan to the East Coast of the United States without refueling, a feat that was also achieved by the German U-boat U-47. The I-400 was also equipped with advanced air conditioning and ventilation systems, which were designed to maintain a comfortable environment for the crew, similar to those used on the United States Navy's USS Nautilus (SSN-571).

● Armament

The I-400 was armed with eight 533mm torpedo tubes, which were capable of launching Type 95 torpedoes, similar to those used on the Japanese destroyer Kagero. The I-400 was also equipped with a 140mm gun, which was used for surface attacks, similar to the Japanese cruiser Mogami. The I-400's main armament, however, was its three Aichi M6A Seiran floatplane bombers, which were carried in a hangar on the submarine's deck, similar to the Japanese aircraft carrier Ryujo. The Seiran bombers were designed to attack enemy ships and coastal installations, and were equipped with Type 99 bombs, similar to those used on the Japanese bomber Mitsubishi G4M.

● Legacy

The I-400 was surrendered to the United States Navy on August 27, 1945, and was later taken to the United States for study and evaluation, where it was examined by Rear Admiral Hyman G. Rickover, who was impressed by its advanced design and technology. The I-400's design influenced the development of post-war submarines, including the United States Navy's USS Triton (SSRN-586) and the Soviet submarine K-222. The I-400 is now on display at the National Museum of the United States Navy in Washington, D.C., where it is recognized as a significant example of Imperial Japanese Navy technology and innovation, alongside other notable ships such as the Japanese battleship Mikasa and the Japanese aircraft carrier Akagi. The I-400's legacy extends beyond its technical achievements, as it also represents the Imperial Japanese Navy's efforts to develop advanced naval technology during World War II, including the Japanese submarine I-13 and the Japanese submarine I-14.