Sinkyo Maru began life as a civilian cargo steamer, built by the Uraga Dock Company in Uraga, Kanagawa. Her keel was laid on February 25, 1932; she launched on November 24 and was completed on April 11, 1933. She was a modest vessel, powered by a three-cylinder triple-expansion steam engine augmented by an exhaust turbine that drove the same propeller shaft through double reduction gearing. Her owners, Chosen Yusen KK, registered her at Jinsen in Japanese-controlled Korea -- modern-day Incheon, South Korea. Through the 1930s she worked the unglamorous trade routes between Korea and the ports of Honshu, with occasional voyages to Vladivostok. In 1938, the romanization of her name changed from Shinkyo Maru to Sinkyo Maru, a bureaucratic footnote that would outlast the ship herself.

On September 15, 1940, the Japanese Navy requisitioned Sinkyo Maru. Within weeks she was attached to the Sasebo Naval District as an auxiliary gunboat, armed with three 12cm naval guns, machine guns, depth charge racks, and 32 depth charges. By January 1941, she was laying mines -- 115 Type 93 mines deployed in two minefields off the Japanese coast. She patrolled Chinese waters, formed part of the Sasebo Local Defence Squadron, and in January 1942 survived a collision with the auxiliary oiler Akatsuki Maru that badly damaged her bridge. Repaired and reassigned, she spent months operating from Kakeromajima in the Amami Islands, south of Kyushu. When the troopship Atsuta Maru was crippled by an American submarine in May 1942, Sinkyo Maru was part of the flotilla that responded -- making anti-submarine sweeps and rescuing survivors while Atsuta Maru burned and eventually sank.

In late 1942, Sinkyo Maru was assigned to reinforce the Japanese campaign in New Guinea. She joined convoys carrying the 20th and 41st Divisions to Wewak -- dangerous runs through waters increasingly dominated by American submarines and aircraft. In January 1943, she embarked 399 troops and 300 bundles of supplies in Busan, sailed to Palau, and from there joined a three-ship echelon escorted by a destroyer for the dash to Wewak. The echelon arrived at 2:00 in the morning, disembarked its cargo in nine hours, and fled before daylight could bring American air attacks. A second run in February followed the same pattern: load in Tsingtao, stage through Palau, sprint to Wewak, and run. By spring 1943, she was reassigned to coastal defense of eastern Japan, patrolling from Yokosuka north to Kushiro on Hokkaido and out to Paramushiro in the Kuril Islands -- the cold, fog-shrouded volcanic chain at the northern limit of Japanese territory.

After a late-1943 refit at Mitsubishi Heavy Industries' shipyard in Yokohama, Sinkyo Maru was redesignated as an auxiliary transport and sent south again. She joined convoys through Okinawa, Taiwan, and on to Manila, arriving in mid-March 1944. On March 20, she departed Manila in Convoy H-22, bound for Halmahera in the Maluku Islands with seven other ships and two escorts. On March 23, in the Basilan Strait, an auxiliary submarine chaser joined the convoy. The next day, off Mindanao, USS Bowfin found them. The submarine's radar picked up the convoy, and at 23:48 Bowfin fired her first salvo. Bengal Maru went down. Minutes later, another salvo struck Sinkyo Maru. She sank in three minutes -- too fast for any organized evacuation. Twelve crew and forty-nine passengers died in those waters, their ship joining the thousands of vessels that the Pacific War scattered across the ocean floor. Sinkyo Maru had been many things in her twelve years: freighter, gunboat, minelayer, troop transport, submarine chaser. In the end, she was just another target in a submarine's crosshairs.