Type B1 submarine

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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
Scrapped: 1
General characteristics
Class & type: Cruiser submarine
  • 2,631 tonnes (2,589 long tons) surfaced
  • 3,713 tonnes (3,654 long tons) submerged
Length: 108.7 m (356 ft 8 in) overall
Beam: 9.3 m (30 ft 6 in)
Draft: 5.1 m (16 ft 9 in)
Installed power:
  • 23.5 knots (43.5 km/h; 27.0 mph) surfaced
  • 8 knots (15 km/h; 9.2 mph) submerged
  • 14,000 nmi (26,000 km; 16,000 mi) at 16 knots (30 km/h; 18 mph) surfaced
  • 96 nmi (178 km; 110 mi) at 3 knots (5.6 km/h; 3.5 mph) submerged
Test depth: 100 m (330 ft)
Crew: 94
Aircraft carried: 1 × floatplane
Aviation facilities: 1 × catapult

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?) was the first group of boats of the Type B cruiser submarines built for the Imperial Japanese Navy (IJN) during the 1940s. In total 20 were built, starting with I-15, which gave the series their alternative name.

Design and description

The Type B submarines were derived from the earlier KD6 sub-class of the Kaidai class and were equipped with an aircraft to enhance their scouting ability. They displaced 2,631 tonnes (2,589 long tons) surfaced and 3,713 tonnes (3,654 long tons) submerged. The submarines were 108.7 meters (356 ft 8 in) long, had a beam of 9.3 meters (30 ft 6 in) and a draft of 5.1 meters (16 ft 9 in). They had a diving depth of 100 meters (330 ft).[1]

For surface running, the boats were powered by two 6,200-brake-horsepower (4,623 kW) diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 1,000-horsepower (746 kW) electric motor. They could reach 23.6 knots (43.7 km/h; 27.2 mph) on the surface and 8 knots (15 km/h; 9.2 mph) underwater.[2] On the surface, the B1s had a range of 14,000 nautical miles (26,000 km; 16,000 mi) at 16 knots (30 km/h; 18 mph); submerged, they had a range of 96 nmi (178 km; 110 mi) at 3 knots (5.6 km/h; 3.5 mph).[3]

The boats were armed with six internal bow 53.3 cm (21.0 in) torpedo tubes and carried a total of 17 torpedoes. They were also armed with a single 14 cm (5.5 in) deck gun and two single mounts for 25 mm (1 in) Type 96 anti-aircraft guns.[3] In the Type Bs, the aircraft hangar was faired into the base of the conning tower. A single catapult was positioned on the forward deck. Late in the war, some of the submarines had their aircraft hangar replaced, to replace it with an additional 14 cm gun. In 1944, I-36 and I-37 had their aircraft hangar and catapult removed so that they could carry four Kaiten manned torpedoes, with I-36 later being further modified to carry six.[3]


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[4] 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


  1. Bagnasco, p. 189
  2. Chesneau, p. 200
  3. 3.0 3.1 3.2 Carpenter & Dorr, p. 102
  4. Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).
  5. 5.0 5.1 Boyd, Carl; Akihiko Yoshida (2002). The Japanese Submarine Force and World War II. Naval Institute Press. ISBN 1-55750-015-0.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  6. Rohwer, Jürgen; Hümmelchen, Gerhard (2005). Chronology of the War at Sea : 1939-1945 : the Naval History of World War II (3. rev. ed.). Annapolis, Md.: Naval Institute Press. p. 289. ISBN 9781591141198.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  7. report of the sinking of I-35, Department of Defence (Australia), undated World War II, accessed 24 April 2010


  • Bagnasco, Erminio (1977). Submarines of World War Two. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-962-6.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  • Boyd, Carl & Yoshida, Akikiko (2002). The Japanese Submarine Force and World War II. Annapolis, Maryland: Naval Institute Press. ISBN 1-55750-015-0.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  • Carpenter, Dorr B. & Polmar, Norman (1986). Submarines of the Imperial Japanese Navy 1904–1945. London: Conway Maritime Press. ISBN 0-85177-396-6.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  • Chesneau, Roger, ed. (1980). Conway's All the World's Fighting Ships 1922–1946. Greenwich, UK: Conway Maritime Press. ISBN 0-85177-146-7.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  • Hashimoto, Mochitsura (1954). Sunk: The Story of the Japanese Submarine Fleet 1942 – 1945. Colegrave, E.H.M. (translator). London: Cassell and Company. ASIN B000QSM3L0.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  • Stille, Mark (2007). Imperial Japanese Navy Submarines 1941-45. New Vanguard. 135. Botley, Oxford, UK: Osprey Publishing. ISBN 978-1-84603-090-1.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>