Type B1 submarine

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Type B1 submarine I-25
Class overview
Name: B1 class
Operators: Japanese Navy EnsignImperial Japanese Navy
Preceded by: Type J3 submarine
Succeeded by: Type B2 submarine
Completed: 18
Lost: 17
General characteristics
Displacement: 2,584 tons surfaced
3,654 tons submerged
Length: 356.5 ft (108.7 m)
Beam: 30.5 ft (9.3 m)
Draft: 16.8 ft (5.1 m)
Propulsion: 2 diesels: 12,400 hp (9,200 kW)
Electric motors: 2,000 hp (1,500 kW)
Speed: 23.5 knots (44 km/h) surfaced
8 knots (15 km/h) submerged
Range: 14,000 nautical miles (26,000 km) at 16 knots (30 km/h)
Test depth: 100 m (330 ft)
Complement: 94 officers and men
Armament: 6 × 533 mm forward torpedo tubes

17 torpedoes

1 × 140 mm 50 calibre gun
Aircraft carried: 1 Yokosuka E14Y seaplane

The Type B1 submarine (巡潜乙型潜水艦 Junsen Otu-gata sensuikan, "Cruiser submarine type B"?), also called I-15-class submarine (伊一五型潜水艦 I-jū-go-gata sensuikan?) were the most numerous submarine class of the Imperial Japanese Navy during World War II. In total 20 were built, starting with I-15, which gave the series their alternative name.

These submarines were fast, had a very long range, and carried a single seaplane, located in a hangar in front of the conning tower, and launched by a catapult. Late in the war, some of the submarines had their aircraft hangar removed, to replace it with a 14 cm gun. In 1944, the I-36 and I-37 were modified so that they could carry four Kaiten manned torpedoes, with I-36 later being further modified to carry six.


The series was rather successful, especially at the beginning of the war.

  • I-17 shelled an oil field up the beach from Santa Barbara and damaged a pump house in Elwood in February 1942. She was sunk by the New Zealand trawler Tui and two US Navy aircraft off Noumea on 19 August 1943.
  • On 15 September 1942 I-19 fired six torpedoes at the aircraft carrier USS Wasp, two of which hit the carrier and destroyed it. The four remaining torpedoes went on for several thousand meters and hit another carrier force, damaging the battleship USS North Carolina, and sinking the destroyer USS O'Brien. She was sunk by the USS Radford[1] on 25 November 1943.
  • I-25 conducted one of the few attacks on the continental United States in September 1942. She was sunk by destroyer USS Patterson off the New Hebrides on 3 September 1943.
  • I-26 sank the US Army chartered merchant ship SS Cynthia Olson about 1,000 miles northeast of Pearl Harbor on 7 December 1941, causing 35 fatalities. She also crippled the aircraft carrier USS Saratoga with one torpedo hit (out of six launched) on 31 August 1942. On 13 November, she also sank the cruiser USS Juneau. She was sunk in action off Leyte in October 1944.
  • I-27 Between June 1942, and February 1944, sank Iron Crown while it was en route Whyalla-Newcastle, sank Fort Mumford and SS Montanan in the Indian Ocean, sank the Liberty ship SS Sambridge and finally the SS Khedive Ismail near the Maldives on February 12, 1944. This last strike was her undoing, as she was sunk by escorting British warships.
  • I-29 was used to conduct personnel and technology exchanges with Germany.


Altogether the Type B submarines (B1, B2, and B3 combined) are credited with sinking 56 merchant ships for a total of 372,730 tonnes, about 35% of all merchant shipping sunk by Japanese submarines during the war.

All B1 type submarines were lost during the conflict, except for I-36, which was scuttled off Gotō Islands by the US Navy on 1 April 1946.

See also[edit]


  1. ^ Cressman, Robert (2000). "Chapter V: 1943". The official chronology of the U.S. Navy in World War II. Annapolis, Maryland: Naval Institute Press. ISBN 978-1-55750-149-3. OCLC 41977179. Retrieved 2012-09-14. 
  2. ^ a b Boyd, Carl; Akihiko Yoshida (2002). The Japanese Submarine Force and World War II. Naval Institute Press. ISBN 1-55750-015-0. 
  3. ^ Rohwer, Jürgen; Hümmelchen, Gerhard (2005). Chronology of the War at Sea : 1939-1945 : the Naval History of World War II (3. rev. ed. ed.). Annapolis, Md.: Naval Institute Press. p. 289. ISBN 9781591141198. 
  4. ^ report of the sinking of I-35, Department of Defence (Australia), undated World War II, accessed 24 April 2010