The Ro-100 class was a medium-sized, coastal submarine derived from the preceding Kaichū type. They displaced 611 tonnes (601 long tons) surfaced and 795 tonnes (782 long tons) submerged. The submarines were 60.9 meters (199 ft 10 in) long, had a beam of 6 meters (19 ft 8 in) and a draft of 3.51 meters (11 ft 6 in). They had a double hull and a diving depth of 75 meters (246 ft).[2]
For surface running, the boats were powered by two 500-brake-horsepower (373 kW) diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 380-horsepower (283 kW) electric motor. They could reach 14.2 knots (26.3 km/h; 16.3 mph) on the surface and 8 knots (15 km/h; 9.2 mph) underwater. On the surface, the Ro-100s had a range of 3,500 nautical miles (6,500 km; 4,000 mi) at 12 knots (22 km/h; 14 mph); submerged, they had a range of 60 nmi (110 km; 69 mi) at 3 knots (5.6 km/h; 3.5 mph).[3]
Upon commissioning, Ro-117 was attached formally to the Yokosuka Naval District and was assigned to Submarine Squadron 11 for workups.[5]
First war patrol
Ro-117 got underway from Japan on 31 March 1944 along with the submarine Ro-116 for her first war patrol, ordered to intercept an Alliedtask force operating in the vicinity of the Palau Islands.[5] She did not find the task force, and returned to Japan on 13 April 1944.[5]
Second war patrol
On 4 May 1944, Ro-117 was reassigned to Submarine Division 51 in Submarine Squadron 7 in the 6th Fleet.[5] She departed Kure, Japan, on 15 May 1944, called at Saipan in the Mariana Islands from 24 to 26 May 1944, then proceeded to Truk, which she reached on 31 May 1944.[5]
Ro-117 got underway from Truk on 4 June 1944 for her second war patrol with orders to join a submarine patrol line north of New Ireland.[5] On 13 June 1944 the Combined Fleet activated Operation A-Go for the defense of the Mariana Islands, and that day the commander-in-chief of the 6th Fleet, Vice AdmiralTakeo Takagi, ordered all available submarines to deploy east of the Marianas.[5] On 14 June 1944, Ro-117 received orders to proceed at flank speed to a new patrol area off the Marianas east of Guam.[5]
The Battle of Saipan began with U.S. landings on Saipan on 15 June 1944.[5] That day, the 6th Fleet ordered most of its submarines, including Ro-117, to withdraw from the Marianas.[5] On 16 June 1944, Ro-117 was ordered to join Patrol Unit C along with the submarines Ro-113, Ro-115, and Ro-116.[5]Ro-117 specifically was directed to patrol southeast of Tinian between the patrol areas of Ro-111 and Ro-113.[5]
Ro-117 was ordered to return to Truk on 22 June 1944 but did not respond.[5] On 12 July 1944, the Imperial Japanese Navy declared her to be presumed lost off Saipan with all 55 men on board.[5] The Japanese struck her from the Navy list on 10 August 1944.[5]
Notes
^ ab"RO-117". IJN Submarine Service – Ijnsubsite.info. Retrieved 8 June 2023.
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 (2016). "IJN Submarine RO-117: Tabular Record of Movement". SENSUIKAN! Stories and Battle Histories of the IJN's Submarines. Combinedfleet.com. Retrieved 5 October 2020.
