I-37, originally numbered I-49, was a Japanese Type B1 submarine in service with the Imperial Japanese Navy during World War II.Boyd, Carl & Yoshida, Akikiko (2002). The Japanese Submarine Force and World War II. Annapolis, Maryland: Naval Institute Press. . 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 .
On 19 June 1943, I-37 hit the 7,176-ton American Liberty ship — bound from Fremantle, Australia, to Bandar Shapur with an 8,200-ton Lend-Lease cargo of fighter aircraft, tanks, and explosives destined for the Soviet Union — with one torpedo in her port side at . The torpedo detonated the explosives in her No.3 hold, and the explosion showered burning debris over Henry Knox, bringing her to a stop and setting her deck cargo and catwalk on fire. At 19:07, her crew abandoned ship, with 25 crewmen and United States Navy Armed Guard personnel losing their lives in the explosion, the fire, and shark attacks, and after several explosions, Henry Knox sank by the bow at around 22:00. Meanwhile, I-37 surfaced, hove to, and ordered the chief mate's lifeboat alongside. Her navigator interrogated the survivors in the boat about their cargo, route, and destination, and about any Allied vessels they had encountered in the area, after which the Japanese ordered the men in the lifeboat to pass various items to I-37 via a handline. The Japanese confiscated the lifeboat's sails, nautical charts, some of its rations, and a flashlight, but returned personal items, matches, and liquor to the lifeboat before departing the area. The survivors then made for the Maldives in several groups. Before the last of them reached land on 30 June 1943, 13 of Henry Knox′s 42 merchant mariners and 13 of her 25 Navy Armed Guards personnel had died. The survivors from the boat that had gone alongside I-37 reported that she had a hangar and a degaussing coil, that her diesel engines started without hesitation — indicating that the engines were in excellent condition and were using high-quality diesel fuel — and that a stereoscopic camera equipped with a filtering mechanism was mounted on her conning tower.
By 1 July 1943, I-37 was part of the Advance Force, as was the rest of Submarine Squadron 8 (the submarines , , , and ). On 9 July, she conducted a reconnaissance of the coast of the Persian Gulf. She returned to Penang on 17 August 1943.
August–September 1943
I-37 departed Penang on 22 August 1943 and moved to Singapore. She set out from Singapore on 5 September 1943 for the return voyage to Penang. On 12 September 1943, she was reassigned to the Southwest Area Fleet.
Second war patrol
I-37 got underway from Penang in mid-September 1943 to begin her second war patrol, again in the Indian Ocean, with an embarked Yokosuka E14Y1 (Allied reporting name "Glen") floatplane, but soon thereafter one of her crewmen came down with appendicitis, and she returned to Penang to seek medical attention for him. She then set out again on 20 September 1943 to begin the patrol, assigned a patrol area in the Mozambique Channel and the vicinity of Mombasa, British East Africa. On 28 September, the British Admiralty sent a message based on Ultra information to Allied forces in the area warning them of the possibility that Japanese submarine-based seaplanes would conduct reconnaissance flights in the Gulf of Aden, Gulf of Oman, and an area west of 54 degrees East between 1 degree 30 minutes North and 1 degree South. On 11 October 1943, I-37′s floatplane reconnoitered the harbor at Diego Suarez, Madagascar, its crew reporting the anchorage to be heavily guarded.
Northwest of Madagascar, I-37 torpedoed and sank the Greek 3,404-gross register ton merchant ship on 23 October 1943. She reported that she attacked two Allied merchant ships in the Mozambique Channel southeast of Pemba Island, one on 4 November 1943 which probably was the 2,850-gross register ton Norwegian steamer , and a different ship during the afternoon of 5 November, and that each time she fired one torpedo, which missed the target. Some historians since have suggested that I-37 actually attacked Hallbyørg twice and fired three torpedoes on each occasion. On 17 November 1943, I-37′s floatplane flew a reconnaissance mission over Kilindini Harbour at Mombasa.
Just after sunset on 27 November 1943, at 12:40 Zulu Time, I-37 torpedoed the Norwegian 9,972-gross register ton armed tanker , which had separated from Convoy PB-64 to proceed independently during a voyage from Bahrain to Melbourne, Australia, with a cargo of diesel oil. A torpedo hit Scotia′s starboard quarter, disabling her steering and bringing her to a stop, and she took on a 15-degree starboard list. Her crew abandoned ship while her first engineer and radio operator remained aboard to transmit an SSS signal, a variant of the SOS signal indicating distress due to submarine attack. I-37 fired another torpedo at Scotia which hit her in her starboard engine room at around 12:55 Zulu Time and broke her in two. Her stern section immediately sank at , but the bow section remained afloat. I-37 surfaced and opened gunfire on it, sinking it as well. took Scotia′s master aboard as a prisoner-of-war. One survivor later testified that I-37′s crew fired at his lifeboat with a submachine gun, killing eight men. On 29–30 November 1943, the patrol vessel rescued 31 survivors. I-37 returned to Penang on 5 December 1943.
December 1943–January 1944
On 12 December 1943, I-37 departed Penang bound for Singapore, which she reached on 13 December. On 15 December, she went into drydock at the naval base at Seletar in Singapore for an overhaul; the same day, Submarine Division 14 was abolished and she was attached directly to the 8th Fleet. She undocked on 18 December 1943 and embarked provisions, and on 27 December 1943 received a new commanding officer, Commander Hajime Nakagawa. She departed Singapore on 12 January 1944 and set course for Penang, where she arrived on 15 January 1944. In early February 1944, most of her officers left her for new assignments, and new officers replaced them. A former crewmember of I-37 later testified that Nakagawa received authorization from the Commander of Submarine Squadron 8 to carry out reprisals against the crews of Allied armed merchant ships in retaliation for the alleged slaughter of Japanese merchant ship crews by Allied submarines.
Third war patrol
With a Yokosuka E14Y1 (Allied reporting name "Glen") floatplane embarked, I-37 got underway from Penang on 10 February 1944 to begin her third war patrol, heading for a patrol area in the Indian Ocean in the Madagascar area. At 00:30 on 14 February, she sighted an Allied merchant ship south of Ceylon and pursued it on the surface for hours. The ship was making at least and, unable to overtake it, I-37 finally discontinued the chase at 01:00 on 15 February.
On 22 February 1944, I-37 attacked the British 7,118-gross register ton armed tanker — which had departed Melbourne on 1 February 1944 to steam in ballast to AbadanEdwards, p. 81. — in the Indian Ocean south of Addu Atoll in the Maldives, firing two torpedoes at her.Edwards, p. 89. British Chivalry′s crew sighted I-37′s periscope and the approaching torpedoes; she began an evasive turn, and one torpedo passed astern of her, but the other hit her in her starboard side. The torpedo hits knocked out British Chivalry′s engines, destroyed two of her lifeboats, and killed six members of her crew.Edwards, pp. 90, 91. Her 53 surviving crewmen abandoned ship in her two remaining lifeboats, one of them motorized.Edwards, p. 90. While the motorized lifeboat began the process of collecting provisions from four uninhabited life rafts cast overboard before British Chivalry′s crew abandoned ship,Edwards, pp. 91, 92. I-37 surfaced either or Edwards, p. 91. away from British Chivalry (according to different sources) and fired seventeen rounds at her. The first six landed near the lifeboat with British Chivalry′s master, Captain Walter Hill, aboard, and then I-37′s gunners concentrated on British Chivalry, scoring three hits as I-37 closed to a range of less than . I-37 then fired another torpedo which hit British Chivalry in her port side admidships, sinking her at 11:30 at .