The submarines of the K6 sub-class were versions of the preceding K5 sub-class with greater range and diving depth.^[1] They displaced 1,133 tonnes (1,115 long tons) surfaced and 1,470 tonnes (1,447 long tons) submerged. The submarines were 80.5 meters (264 ft 1 in) long, had a beam of 7 meters (23 ft 0 in) and a draft of 4.07 meters (13 ft 4 in). They had a diving depth of 80 meters (260 ft).^[2]

For surface running, the boats were powered by two 2,100-brake-horsepower (1,566 kW) diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 600-horsepower (447 kW) electric motor.^[3] They could reach 19.75 knots (36.58 km/h; 22.73 mph) on the surface and 8 knots (15 km/h; 9.2 mph) underwater. On the surface, the K6s had a range of 11,000 nautical miles (20,000 km; 13,000 mi) at 12 knots (22 km/h; 14 mph); submerged, they had a range of 45 nmi (83 km; 52 mi) at 5 knots (9.3 km/h; 5.8 mph).^[1]

The boats were armed with four internal bow 53.3 cm (21.0 in) torpedo tubes and carried a total of ten torpedoes. They were also armed with a single 76.2 mm (3.00 in) L/40 anti-aircraft gun and two single 25 mm (1.0 in) AA guns.^[1]

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]

First war patrol edit

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]

Second war patrol edit

During the second half of December 1943, Ro-37 took aboard supplies from the auxiliary submarine tender Heian Maru 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]

Loss edit

Ro-37 was 155 nautical miles (287 km; 178 mi) southeast of San Cristobal in the Solomon Islands on 22 January 1944 when she sighted the United States Navy fleet oiler USS Cache (AO-67), which was on a voyage to Espiritu Santo in the New Hebrides in company with the destroyer minesweeper USS Southard (DMS-10).^[4] She hit Cache in the port side with one torpedo at 12°08′S 164°23′E / 12.133°S 164.383°E / -12.133; 164.383.^[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 USS Buchanan (DD-484) — 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 12,750 yards (11,660 m) with what her commanding officer described as a "fairly large" submarine on the surface 130 nautical miles (240 km; 150 mi) east-southeast of San Cristobal and 95 nautical miles (176 km; 109 mi) northwest of where Ro-37 had torpedoed Cache.^[4] After closing to a range of 2,000 yards (1,800 m), 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 1,250 yards (1,140 m).^[4] Buchanan dropped 53 depth charges over the next three hours and finally sank Ro-37 at 11°47′S 164°17′E / 11.783°S 164.283°E / -11.783; 164.283 (Ro-37).^[4] Buchanan′s crew observed an oil slick covering 5 square miles (13 km²) 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]

• Bagnasco, Erminio (1977). Submarines of World War Two. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-962-6.
• Carpenter, Dorr B. & Polmar, Norman (1986). Submarines of the Imperial Japanese Navy 1904–1945. London: Conway Maritime Press. ISBN 0-85177-396-6.
• Chesneau, Roger, ed. (1980). Conway's All the World's Fighting Ships 1922–1946. Greenwich, UK: Conway Maritime Press. ISBN 0-85177-146-7.
• Hackett, Bob; Kingsepp, Sander (2017). "IJN Submarine RO-37: Tabular Record of Movement". SENSUIKAN! Stories and Battle Histories of the IJN's Submarines. Combinedfleet.com. Retrieved 20 September 2020.
• Hackett, Bob; Sander Kingsepp (2003). "Kaichu Type". Sensuikan!. Combinedfleet.com. Retrieved 20 September 2020.
• Hashimoto, Mochitsura (1954). Sunk: The Story of the Japanese Submarine Fleet 1942 – 1945. Colegrave, E.H.M. (translator). London: Cassell and Company. ASIN B000QSM3L0.