Military Wiki
Type B1 submarine
Type B1 submarine I-25
Class overview
Name: B1 class
Operators: Japanese Navy EnsignImperial Japanese Navy
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

6 × 533 mm forward torpedo tubes
17 torpedoes

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

The Type B1 submarine (also known as the I-15 series) 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 a US Army chartered Schooner Cynthia Olson 7 December 1941, causing 35 fatalities. She crippled the aircraft carrier USS Saratoga with one torpedo hit (out of six launched) on 31 August 1942. On 13 November, she also destroyed the cruiser USS Juneau. She was sunk in action off Leyte in October 1944.
  • I-29 was used to conduct personnel and technology exchanges with Germany.


  • I-15 was sunk off San Cristobol on 2 November 1942 by destroyer USS McCalla.
  • I-19 was sunk by USS Radford 25 November 1943
  • I-21 made her final report on 27 November 1943, off the Gilbert Islands, following which she was never heard from again.[2] Some sources say she was sunk by aircraft from escort carrier USS Chenango on 29 November 1943.[citation needed]
  • I-23 was lost in February 1942, following a final report made from off Oahu.
  • I-25 was sunk by USS Patterson on 25 August 1943.
  • I-27 was sunk by the British destroyers HMS Paladin and HMS Petard off Addu Atoll on 12 February 1944 after it had sunk the troopship SS Khedive Ismail with the loss of about 1,300 lives. She was first rammed by Paladin then torpedoed by Petard.[2]
  • I-28 was sunk by submarine USS Tautog south of Truk on 17 May 1942.
  • I-29 was sunk by USS Sawfish in Balintang Channel on 26 July 1944.
  • I-30 was the first Japanese submarine to reach Europe under the Yanagi missions, but she was sunk by a mine off Singapore on 13 October 1942.
  • I-31 was sunk by destroyers USS Edwards and USS Farragut off Kiska on 12 May 1943.
  • I-32 was sunk by the destroyer escort USS Manlove and the subchaser USS Canastota south of Wotje on 24 March 1944.
  • I-33 was lost during sea trials in the Inland Sea on 13 June 1944.
  • I-34 was sunk by submarine HMS Taurus off Penang on 13 November 1943.
  • I-35 was sunk by destroyers USS Meade and USS Frazier off Tarawa on 23 November 1943.[3]
  • I-37 was sunk by destroyer escorts USS Conklin and USS McCoy Reynolds off Leyte on 19 November 1944.
  • I-38 was sunk by destroyer USS Nicholas near Yap on 12 November 1944.
  • I-39 was sunk by destroyer USS Boyd in the Gilberts on 26 November 1943.

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.


  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. 2.0 2.1 Boyd, Carl; Akihiko Yoshida (2002). The Japanese Submarine Force and World War II. Naval Institute Press. ISBN 1-55750-015-0. 
  3. report of the sinking of I-35, Department of Defence (Australia), undated World War II, accessed 24 April 2010

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