Nankai (Japanese: Ã¥ÂÂæµ·) was originally named Regulus, a Dutch auxiliary minelayer built for the during the Second World War. The ship was launched a few days after the start of the Pacific War in December 1941. Still incomplete, she was scuttled by the Dutch in March 1942 to prevent her capture by the Japanese, but the Imperial Japanese Navy refloated the ship and converted her into a gunboat.
The Ram-class ships had a standard displacement of . They measured long overall with a beam of and a draught of . The minelayers were powered by two diesel engines, each driving one propeller shaft. They had a maximum speed of . The Ram class had a complement of 120 officers and ratings.
The Dutch intended the ship to be armed with three anti-aircraft (AA) guns, but the Japanese rearmed Nankai with two Type 10 AA guns, four Type 96 AA guns and an unknown number of depth charges or mines.
She was laid down in 1941 at the Droogdok Maatschappij Soerabaja as an auxiliary minelayer for the benefit of the named Regulus. She was scuttled before completion by Dutch forces on 2 March 1942 after the Japanese occupation of the Dutch East Indies. She was seized by the Japanese, repaired and rebuilt as a gunboat. The ship was launched on 21 April 1943 under the name of Nankai and was completed on 7 June 1944.
On 21 September 1944, Nankai departed Surabaya, Java, escorting transport . On 23 September 1944, Nankai and Hokkai Maru both struck mines laid by the submarine , west of Sebuku Island at , leaving both ships crippled. Nankai and Hokkai Maru were towed and repaired at the No. 102 Naval Construction and Repair Department at Surabaya.
On 16 July 1945, while being escorted by the CH-1, she was torpedoed and sunk by at , west of Surabaya. Nankai was struck from the Navy List on 30 July 1945.