The Japanese called these ships Kaibōkan, "ocean defence ships", (Kai = sea, ocean, Bo = defence, Kan = ship), to denote a multi-purpose vessel. They were initially intended for patrol and fishery protection, minesweeping and as convoy escorts. The ships measured 77.72m (254.99feet) overall, with a beam of 9.1m (29.9feet) and a draft of 3.05m (10.01feet).[1] They displaced 860sp=usNaNsp=us at standard load and 1020sp=usNaNsp=us at deep load. The ships had two diesel engines, each driving one propeller shaft, which were rated at a total of 4200bhp for a speed of 19.7kn. The ships had a range of 8000nmi at a speed of .[2]
The main armament of the Shimushu class consisted of three Type 3 1201NaN1 guns in single mounts, one superfiring pair aft and one mount forward of the superstructure. They were built with four Type 96 251NaN1 anti-aircraft guns in two twin-gun mounts, but the total was increased to 15 guns by August 1943. A dozen depth charges were stowed aboard initially, but this was doubled in May 1942 when their minesweeping gear was removed.[2] The anti-submarine weaponry later rose to 60 depth charges with a Type 97 811NaN1 trench mortar and six depth charge throwers.
In July 1943 Kunashiri participated in the Kiska evacuation aspect of Operation Ke. During the war Kunashiri operated mostly in the Kuriles and Hokkaido area escorting various convoys. On 28 July 1944. she was reported "damaged" by unknown cause- . After the end of World War II Kunashiri returned to Sasebo and was later used by the Allied Repatriation Service. On 4 June 1946 while en route to Uraga the vessel ran aground and was later abandoned. In attempts to rescue her, the also ran aground, while at the same time, she too was repatriating Japanese troops from Singapore.[3]