Japanese submarine I-31

The Japanese submarine I-31 was one of 20 Type B cruiser submarines of the B1 sub-class built for the Imperial Japanese Navy (IJN) during the 1940s.

Design and description
The Type B submarines were derived from the earlier KD6 sub-class of the Kaidai-class submarine and were equipped with an aircraft to enhance their scouting ability. They displaced 2589 LT surfaced and 3654 LT submerged. The submarines were 108.7 m long, had a beam of 9.3 m and a draft of 5.1 m. They had a diving depth of 100 m.

For surface running, the boats were powered by two 6200 bhp diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 1000 hp electric motor. They could reach 23.6 kn on the surface and 8 kn underwater. On the surface, the B1s had a range of 14000 nmi at 16 kn; submerged, they had a range of 96 nmi at 3 kn.

The boats were armed with six internal bow 53.3 cm torpedo tubes and carried a total of 17 torpedoes. They were also armed with a single 140 mm/40 deck gun and two single mounts for 25 mm Type 96 anti-aircraft guns. 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.

Career
In November 1942, I-31 was spotted doing reconnaissance with its seaplane off Suva, Fiji.

On 12 May 1943 I-31 attacked the USS Pennsylvania and the USS Santa Fe (CL-60) with torpedoes nine miles northeast of Holtz Bay, all missed. On 12 May 1943, near Holtz Bay, Attu, her periscope was sighted by American destroyers, USS Edwards (DD-619) and USS Frazier (DD-607), who immediately opened fire. I-31 dove quickly but not before Edwards scored hits. The destroyers quickly made sonar contact and began a series of depth charge attacks until, after surviving for 10 hours, she was sunk by Frazier on 13 May.