I-37, originally numbered I-49, was a Japanese Type B1 submarine in service with the Imperial Japanese Navy during World War II. Commissioned in 1943, she made three war patrols, all in the Indian Ocean, during the last of which her crew committed war crimes by massacring the survivors of the merchant ships she sank. Subsequently, converted into a kaiten manned suicide attack torpedo carrier, she was sunk during her first kaiten mission in 1944.
Design
I-37 was long and had a beam of and a draft of . She could dive to She was armed with six internal bow torpedo tubes and carried a total of 17 torpedoes. I-37 was also armed with a single /40 deck gun and two single mounts for Type 96 anti-aircraft guns. Designed as a submarine aircraft carrier, she had a hangar and an aircraft catapult and could carry one Yokosuka E14Y1 (Allied reporting name "Glen") reconnaissance floatplane.
Construction and commissioning
I-37 was laid down at the Kure Naval Arsenal in Kure, Japan, as Submarine No. 150 on 7 December 1940. She was both launched and renumbered I-49 on 22 October 1941, then again renumbered I-37 on 1 November 1941. She was completed and commissioned on 10 March 1943.
Service history
March–June 1943
Upon commissioning, I-37 was attached to the Kure Naval District and assigned to the Kure Submarine Squadron. She passed through the Iyo Nada in the Seto Inland Sea on 13 March 1943, and on 22 March underwent inspection by the staff of the Kure Submarine Squadron. She participated in torpedo practice with the submarines , , and on 26 March. On 1 April 1943, she was reassigned to Submarine Division 11 for work-ups and on 2 April she arrived at Kure for repairs to her attack periscope and retractable short-wave radio antenna. After the completion of her repairs, she took part during May 1943 in testing in the Seto Inland Sea of the Unkato cargo container, a submersible container that could carry up to 377 tons of supplies, designed for a one-way trip in which the cargo's recipients released, recovered, and unloaded it. Workers installed a Type 22 radar aboard her in May 1943.
With her workups and testing completed, I-37 was reassigned to Submarine Division 14 in Submarine Squadron 8 in the 6th Fleet on 23 May 1943. She got underway from Kure on 25 May bound for Penang in Japanese-occupied British Malaya, which she reached on 4 June 1943.
First war patrol
I-37 departed Penang on 8 June 1943 to begin her first war patrol, assigned a patrol area in the Indian Ocean between the Chagos Archipelago and the Persian Gulf. She had her first success on 16 June 1943, when she torpedoed the 8,078-gross register ton British armed motor tanker — which was on a voyage in ballast from Sydney, Australia, to Abadan, Iran — southeast of the Chagos Archipelago. After San Ernesto′s crew abandoned ship at , I-37 briefly opened gunfire on San Ernesto before departing the area with her still afloat. Altogether, two members of San Ernesto′s crew and two of her gunners lost their lives; an American Liberty ship, , rescued San Ernesto′s master and 22 others, while 12 other members of her crew came ashore in another lifeboat on Fanhandu Island in the Maldives on 14 July 1943 after 28 days at sea. The derelict San Ernesto herself remained afloat, drifting across the Indian Ocean before eventually running aground on the west side of Nias Island off Sumatra in the Japanese-occupied Netherlands East Indies at .