The I-201-class submarines were submarines of the Imperial Japanese Navy during World War II. These submarines were of advanced design, built for high underwater speed, and were known as Sentaka-Dai type submarine or Sentaka type submarine. The type name, was shortened to Suichū Kōsoku Sensuikan Ō-gata. They were one of the fastest submarine class built during World War II, second only to Walter Type XVII closed-cycle powered submarines. Twenty-three units were ordered from the Kure Navy Yard under the 1943 construction program. Due to the deteriorating war situation, only eight boats were laid down, and only three, numbered I-201, I-202 and I-203, were completed before the end of the war. None of them saw operational use.
Background
In 1938 the Imperial Japanese Navy constructed an experimental high-speed submarine for evaluation purposes, which was designated Submarine No.71 for security purposes. Based on previous experience with high-speed, short-range midget submarines, Number 71 displaced only 230 tons surfaced with a length of. She could attain a submerged speed of over, making her the fastest submarine of her day. The results gained from experiments with Number 71 formed the basis for the I-201 class submarines.
Design
By late 1942 it had become apparent to the IJN that conventional submarines were unable to survive the new ASW techniques coming into service, such as radar, HF/DF, sonar, and new depth charge projectors. New submarines were required, with a higher underwater than surface speed, quick-diving capability, quiet underwater running, and a high underwater operational radius. The IJN General Staff made an official request for high-speed submarines in October 1943 and among the ships planned in 1944 to be constructed in 1945 were 23 "underwater high speed submarines" temporarily designated "Ships No. 4501-4523". The General Staff's final requirements were stated in Order No. 295 dated 29 October 1943 to the Navy Technical Department. These included an underwater speed of which was reduced to for practical reasons. Nevertheless, they were the fastest operational submarines of World War II, outpacing even the German Type XXI. To meet the requirement for high underwater speed the designers had to:
Adopt a single-hull structure
Locate the main ballast tank higher than previous submarines to give a higher center of gravity and improve dynamic stability
Give the pressure hull and casing a highly streamlined form
Replace fixed deck guns with retractable mounts housed in shuttered recesses when submerged.
Use steel plates for the upper deck rather than wood
Install underwater charging system
Fit large horizontal control surfaces at the stern instead of the more usual bow-mounted dive planes; this improved directional stability and may have decreased turbulence-induced drag.
Reduce the crew and crew accommodation to provide battery space; the Sen-Taka was designed for a crew of 31, compared to that the similar-sized Sen-Chu, and the Kai Dai 1 Types.
Restrict the armament, also to save space; the Sen-Taka had the same torpedo outfit as the smaller Sen-Chu2nd class submarine, and just half that of the comparable Kaidai 1st class submarine. Also the Sen-Taka had no deck gun, and the AA armament carried had to be held in retractable mounts, requiring hull space, in order to meet the streamlining requirement.
The I-201 class bore little resemblance to earlier I-boats, which were optimized for long range and high surfaced speed. By contrast, the I-201 emphasized submerged performance. It featured powerful electric motors, streamlined all-welded hulls, and a large capacity battery consisting of 4,192 cells. The maximum underwater speed of was double that of contemporary American designs. The I-201s, like other Japanese submarines of the period, were also equipped with a crude snorkel, allowing underwater diesel operation while recharging batteries. I-201'' displaced 1,291 tons surfaced and 1,451 tons submerged. It had a test depth of. Armament consisted of four 53 cm torpedo tubes and 10Type 95 torpedoes. The two 25 mm anti-aircraft guns were housed in retractable mounts to maintain streamlining. The submarine was designed for mass production, with large sections prefabricated in factories and transported to the slip for final assembly.
Fate
Two submarines, I-201 and I-203, were seized and inspected by the US Navy at the end of the hostilities. They were part of a group of four captured submarines, including the giant and I-401, which were sailed to Hawaii by US Navy technicians for further inspection. On 26 March 1946, the US Navy decided to scuttle these captured Japanese submarines to prevent the technology from falling into the hands of the Soviet Union. On 5 April 1946, I-202 was scuttled in Japanese waters. On 21 May 1946, I-203 was torpedoed and sunk by submarine off the Hawaiian Islands. On 23 May 1946, I-201 was torpedoed and sunk by. The Hawaii Undersea Research Laboratory found the wreck of the I-201 near Hawaii using submersible craft in 2009.
