Ro-115 was an Imperial Japanese Navy Ro-100-class submarine. Completed and commissioned in November 1943, she served in World War II, operating in the central Pacific Ocean, the New Guinea campaign, the Indian Ocean, and off the Philippine Islands. She was sunk in February 1945 during her fifth war patrol.
Design and description
The Ro-100 class was a medium-sized, coastal submarine derived from the preceding Kaichū type. They displaced surfaced and submerged. The submarines were long, had a beam of and a draft of . They had a double hull and a diving depth of .
For surface running, the boats were powered by two diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a electric motor. They could reach on the surface and underwater. On the surface, the Ro-100s had a range of at ; submerged, they had a range of at .
The boats were armed with four internal bow torpedo tubes and carried a total of eight torpedoes. They were also armed with two single mounts for Type 96 anti-aircraft guns or a single L/40 AA gun.
Construction and commissioning
Ro-115 was laid down as Submarine No. 406 on 12 October 1942 by Kawasaki at Kobe, Japan. She had been renamed Ro-115 by the time she was launched on 19 June 1943. She was completed and commissioned on 30 November 1943.
Service history
November 1943–March 1944
Upon commissioning, Ro-115 was attached to the Yokosuka Naval District and was assigned to Submarine Squadron 11 in the 6th Fleet for workups. On 10 March 1944, she was reassigned to Submarine Division 51 in Submarine Squadron 7 in the 6th Fleet. On 11 March 1944 she departed Kure, Japan, bound for Truk, which she reached on 22 March 1944.
First war patrol
On 28 March 1944, Ro-115 departed Truk to begin her first war patrol, assigned a patrol area in the Pacific Ocean west of Jaluit Atoll. The patrol was uneventful, and she returned to Truk on 18 April 1944. She sortied the same day to intercept an Allied task force Japanese forces had reported, but did not find it, and again returned to Truk on 19 April 1944.
Supply mission and second war patrol
Ro-115 departed Truk on 19 May 1944 to carry supplies to Wewak, New Guinea, in support of Japanese forces fighting in the New Guinea campaign. After calling at Wewak on 27 May 1944 and unloading her cargo, she got back underway the same day and proceeded to Palau, where she arrived on 3 June 1944 to deliver secret Imperial Japanese Army documents including codebooks.
On 7 June 1944, Ro-115 put to sea from Palau to begin her second war patrol, with orders to join a submarine patrol line north of New Ireland. 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 Admiral Takeo Takagi, ordered all available submarines to deploy east of the Marianas. On 14 June 1944, Ro-115 received orders to proceed at flank speed to a new patrol area south of Guam.
The Battle of Saipan began with U.S. landings on Saipan on 15 June 1944. On 16 June 1944, Ro-115 was ordered to join Patrol Unit C along with the submarines , , and . Ro-115 specifically was directed to patrol in the Philippine Sea northwest of Rota in the Marianas. She was northwest of Rota on 19 June 1944 when she sighted two groups of United States Navy aircraft carriers and their escorts, and at 18:07 Japan Standard Time she fired four torpedoes at what her commanding officer described as a "Saratoga-class" aircraft carrier, but they all missed. The escorts subjected her to a brief counterattack with depth charges, but she escaped unscathed and received orders to return to Truk, where she arrived on 27 June 1944.
July–October 1944
On 7 July 1944, Ro-115 left Truk and set course for Yokosuka, Japan, arriving there on 17 July 1944. On 10 August 1944, she departed Yokosuka bound for Penang in Japanese-occupied British Malaya, from which she was to conduct operations in the Indian Ocean. During her voyage to Penang, Submarine Division 51 was disbanded on 15 August 1944 and she and Ro-113 were reassigned to Submarine Squadron 8 at Penang.