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]
Upon commissioning, Ro-50 was attached to the Maizuru Naval District and assigned to Submarine Squadron 11 for workups.[4] She was reassigned to Submarine Division 34 in the 6th Fleet on 5 November 1944.[4]
Ro-50 was in the Philippine Sea 150 nautical miles (280 km; 170 mi) northeast of Luzon′s Lamon Bay on 25 November 1944 when she detected a plane on radar.[4] Believing the plane to have come from a United States Navyaircraft carrier, Ro-50′s commanding officer moved to intercept the carrier.[4] Five hours later, Ro-50 detected propeller noises, and soon thereafter she sighted three aircraft carriers with eight destroyers escorting them in a ring formation.[4] After Ro-50 penetrated the escort screen, she sighted what her commanding officer described as a "Wasp-class" aircraft carrier dead ahead at a range of only 875 yards (800 m).[4] After she fired four torpedoes at the carrier and dived to 263 feet (80 m), her crew heard a large explosion, and five minutes later her sound operator reported hearing the noises of a sinking ship breaking up that lasted for the next two minutes.[4]
Ro-50′s commanding officer claimed to have sunk an escort aircraft carrier and a destroyer in the attack, but postwar analysis disproved his claim, and the explosion and other sounds Ro-50′s crew heard probably were due to premature or end-of-run detonations of her torpedoes.[4] Her target may have been U.S. Navy Task Group 38.3, a component of Task Force 38, because the battleshipUSS Washington(BB-56), operating as a part of that task group, sighted two torpedoes passing ahead of her at the time of Ro-50′s attack, at least one of which appeared to be suffering from a steering problem.[4]Ro-50 returned to Kure on 27 December 1944.[4]
Second war patrol
With 6th Fleet commander-in-chief Vice AdmiralShigeyoshi Miwa on hand to see her off, Ro-50 set out from Kure on 23 January 1945 to begin her second war patrol, again in the Philippine Sea east of Luzon.[4] She was off Leyte on 1 February 1945 when she sighted an Allied ship and pursued it, but she discontinued the chase when she identified it as a hospital ship.[4] On 3 February 1945, she was in the Philippine Sea east of Luzon when an Allied warship — possibly the U.S. destroyer escortUSS Tisdale(DE-33), which reported making a depth-charge attack against a sonar contact that day while on the return leg to Manus Island of a round-trip voyage as a convoy escort[4] — pursued and attacked her.[4] She escaped, but suffered damage.[4]
On 4 February 1945, Ro-50 received orders from the 6th Fleet to stand by to evacuate Imperial Japanese Navy pilots stranded in the Batulinao area of northern Luzon.[4] On 10 February 1945, however, she encountered an Allied convoy steaming in a single column at 08°01′N136°37′E / 8.017°N 136.617°E / 8.017; 136.617 300 nautical miles (560 km; 350 mi) east-southeast of Surigao on Leyte.[4] She fired four torpedoes, one of which struck the tank landing ship USS LST-577, which was on a voyage from Hollandia, New Guinea, to Leyte, at about 08:10.[4] The torpedo exploded, blowing off about a third of LST-577, including her bridge.[4] Steaming a few thousand yards to port of LST-577, the destroyer USS Isherwood(DD-520) began a search for Ro-50 while another tank landing ship prepared to take LST-577 under tow and the rest of the convoy and its escorts departed the area.[4]
Ro-50 surfaced after sundown on 10 February, and at 21:10 Isherwood detected her on radar at a range of 14,000 yards (12,800 m).[4] Working up to 25 knots (46 km/h; 29 mph), Isherwood closed to 1,500 yards (1,400 m) and turned on her searchlights, but none could bear on Ro-50.[4] Seeing the searchlights, Ro-50 crash-dived, descending to 395 feet (120 m).[4]Isherwood then made sound contact on Ro-50 and dropped a full pattern of depth charges at a shallow setting.[4] The explosion of the depth charges damaged Ro-50, rupturing her diving tank valve, shattering the lenses in both of her periscopes, and causing leaks in all of her torpedo tubes.[4]Isherwood dropped two more full patterns of depth charges before losing contact, and her commanding officer and other members of her crew reported smelling oil.[4]
On 14 February 1945, Ro-50 transmitted a situation report to 6th Fleet headquarters and received permission to return to Kure, with orders to conduct a reconnaissance of the Ryukyu Islands en route.[4] An Imperial Japanese Navy floatplane mistakenly attacked her south of Kyushu on 19 February 1945, dropping three depth charges, but she reached Kure on 20 February.[4] She later moved to Maizuru.[4]
Third war patrol
On 20 April 1945, Ro-50 got underway from Maizuru and transited the Bungo Strait to begin her third war patrol, assigned a patrol area in the Philippine Sea off Kitadaitōjima at the northern end of the Daitō Islands southeast of Okinawa.[4] Off Kitadaitōjima on 28 April, she detected the propeller noises of an Allied task force, but was too far away to attempt an attack.[4] She returned to Kure on 4 May 1945, and later moved back to Maizuru.[4]
Fourth war patrol
Ro-50 departed Maizuru on 29 May 1945, heading for an area in the East China Sea east of Formosa for her fourth war patrol.[4] After she arrived in her patrol area on 6 June 1945, she received orders to move to the waters of the Philippine Sea between Okinawa and Ulithi Atoll.[4] Her patrol was uneventful, and she returned to Maizuru on 3 July 1945.[4]
End of war
Ro-50 was still in Japan when EmperorHirohito announced the end of hostilities between Japan and the Allies on 15 August 1945.[4] She was transferred from Submarine Division 34 to Submarine Division 15 that day.[4] The only Kaichu-type submarine to survive World War II,[5] she surrendered to the Allies in September 1945.[4]
Final disposition
The Japanese struck Ro-50 from the Navy list on 30 November 1945.[4] After she was stripped of all useful equipment and material, the U.S. Navy scuttled her along with a number of other Japanese submarines off the Goto Islands on 1 April 1946 in Operation Road's End, sinking her due east of Goto Island, 16 nautical miles (30 km; 18 mi) off Kinai Island.[4]
Bagnasco, Erminio (1977). Submarines of World War Two. Annapolis, Maryland: Naval Institute Press. ISBN0-87021-962-6.
Carpenter, Dorr B. & Polmar, Norman (1986). Submarines of the Imperial Japanese Navy 1904–1945. London: Conway Maritime Press. ISBN0-85177-396-6.
Chesneau, Roger, ed. (1980). Conway's All the World's Fighting Ships 1922–1946. Greenwich, UK: Conway Maritime Press. ISBN0-85177-146-7.
Hackett, Bob; Kingsepp, Sander (2017). "IJN Submarine RO-50: Tabular Record of Movement". SENSUIKAN! Stories and Battle Histories of the IJN's Submarines. Combinedfleet.com. Retrieved 26 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.
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