The submarines of the K6 sub-class were versions of the preceding K5 sub-class with greater range and diving depth. They displaced 11150NaN0 surfaced and 14470NaN0 submerged. The submarines were 80.5m (264.1feet) long, had a beam of 7m (23feet) and a draft of 4.07m (13.35feet). They had a diving depth of 80m (260feet).[1]
For surface running, the boats were powered by two 21000NaN0 diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 600hp electric motor.[2] They could reach 19.75kn on the surface and underwater. On the surface, the K6s had a range of 11000nmi at ; submerged, they had a range of 45nmi at .
The boats were armed with four internal bow 53.3cm (21inches) torpedo tubes and carried a total of ten torpedoes. They were also armed with a single 76.2mm L/40 anti-aircraft gun and two single 251NaN1 AA guns.[3]
Ro-37 was laid down as Submarine No. 203 on 9 October 1941 by the Sasebo Navy Yard at Sasebo, Japan.[4] She was renamed Ro-37 on 20 June 1942,[4] and was provisionally attached to the Maizuru Naval District that day.[4] She was launched on 30 June 1942[4] and completed and commissioned a year later on 30 June 1943.[4]
Upon commissioning, Ro-37 was attached formally to the Maizuru Naval District and assigned to Submarine Squadron 11 for workups.[4] On 16 September 1943 she was reassigned directly to 6th Fleet headquarters, and she departed Maizuru bound for Truk on 22 September 1943.[4] During her voyage, she was reassigned to Submarine Division 1 in the 6th Fleet on 24 September 1943.[4] She arrived at Truk on 7 October 1943.[4]
Ro-37 got underway from Truk on 20 October 1943 to begin her first war patrol, assigned a patrol area east of the New Hebrides as part of Submarine Group A.[4] While at sea, she was reassigned to Submarine Division 34 on 31 October 1943, but otherwise her patrol was uneventful.[4] She returned to Truk in November 1943.[4]
During the second half of December 1943, Ro-37 took aboard supplies from the auxiliary submarine tender at Truk.[4] On 2 January 1944, Fleet Radio Unit, Melbourne (FRUMEL), an Allied signals intelligence unit headquartered at Melbourne, Australia, reported that a Japanese message transmitted from Truk that FRUMEL had intercepted and decrypted said that Ro-37 was scheduled to depart Truk Lagoon via the South Channel at 16:00 on 3 January 1944 and proceed east-southeast on a course of 116 degrees.[4] As FRUMEL had reported, Ro-37 got underway from Truk on 3 January 1944 on her second war patrol, bound for a patrol area off the New Hebrides.[4] The Japanese never heard from her again.[4]
Ro-37 was southeast of San Cristobal in the Solomon Islands on 22 January 1944 when she sighted the United States Navy fleet oiler, which was on a voyage to Espiritu Santo in the New Hebrides in company with the destroyer minesweeper .[4] She hit Cache in the port side with one torpedo at -12.1333°N 187°W.[4] The explosion opened holes in three of Cache′s oil tanks, damaged other tanks, and blew two men overboard, killing one of them.[4] Southard rescued the other man from the water.[4]
Meanwhile, Cache transmitted a distress signal, which the destroyer — which was on a voyage from Purvis Bay to Espiritu Santo — received.[4] Buchanan put on flank speed to go to Cache′s assistance.[4] Buchanan made radar contact at a range of 12750yd with what her commanding officer described as a "fairly large" submarine on the surface east-southeast of San Cristobal and northwest of where Ro-37 had torpedoed Cache.[4] After closing to a range of 2000yd, Buchanan illuminated Ro-37 with a searchlight in time to see her submerge.[4] Buchanan then detected Ro-37 on sonar at a range of 1250yd.[4] Buchanan dropped 53 depth charges over the next three hours and finally sank Ro-37 at -11.7833°N 181°W.[4] Buchanan′s crew observed an oil slick covering on the surface, and the following morning a large amount of wooden and cork debris was seen floating in the vicinity of the sinking.[4]
On 17 February 1944, the Imperial Japanese Navy declared Ro-37 to be presumed lost in the New Hebrides area with all 61 hands.[4] She was stricken from the Navy list on 30 April 1944.[4]