Gokoku Maru (護國丸) was an armed merchant cruiser of the Imperial Japanese Navy in World War II, the last ship of the Hōkoku Maru class ocean liners. The ship entered service in 1942 and was employed mainly as a troop transport. She came under attack several times during her service career, and was sunk in a submarine attack in November 1944.
Gokoku Maru was laid down at the Tama shipyard in Okayama Prefecture prior to the outbreak of World War II. She was designed as a cargo liner for the Osaka Shosen Lines's regularly scheduled services between Japan and Africa. She was launched in April 1942 and completed in September of that year. During the building process, she was requisitioned by the Imperial Japanese Navy (in July 1942) and converted into an Armed Merchant Cruiser. She was also outfitted as a submarine tender, but was employed mainly as a transport.
After commissioning in September 1942, Gokoku Maru was assigned to a Singapore naval base. In December 1942 as part of Operation Hei-Go, she transported troops and supplies to Madang, New Guinea. During this period, she was attacked by U.S. submarine Albacore. It hit her escort, the cruiser Tenryu, and Gokoku Maru herself was bombed by a U.S. aircraft. In January 1943, en route to Palau, she was hit by a torpedo from the submarine Searaven, but it turned out to be a dud. In February, as part of Operation Hinoe-Go 3, she was fired on by U.S. submarine Runner, but suffered no hits. In July, she was involved in a collision and was forced to return to Japan for repairs.
In October, Gokoku Maru was part of operation Tei-Go 4, taking reinforcements from China to the Pacific theater. The convoy came under attack by a pack of three submarines led by Charles "Swede" Momsen in Cero; Gokoku Maru was fired on by Shad, but suffered no damage. The following month she was bombed by U.S. aircraft near Rabaul, but again escaped injury. In November, she returned to Japan for a refit, but was again attacked, this time by Gurnard, and suffered two torpedo hits. Gokoku Maru survived, but spent the next six months under repair at Yokohama.
In June 1944, she returned to service with convoy Hi-67. This convoy was attacked by U.S. submarine Bang, with two ships damaged, but Gokoku Maru escaped harm. In July, near Davao, she was torpedoed by Dace, scoring two hits, but both failed to explode. In August, she was part of convoy Hi-72 to Manila, returning in September. During this voyage, she was bombed and suffered one hit.
After temporary repairs, Gokoku Maru continued to operate, but in November, while en route to Sasebo for repair, she was found by U.S. submarine Barb. She was hit by two torpedoes and badly damaged. When she tried to escape, Gokoku Maru was hit again, and this time the damage was fatal; she sank on 10 November 1944 off Koshiki Jima, Kyushu, Japan with the loss of 326 crew and passengers.
- Gokoku Maru Tabular Record of Movement B Hackett, S Kingsepp 1998-2014; retrieved 18 December 2018
- "USS BARB SS 220". Pigboats.com. Retrieved 9 January 2016.
- LaVO, Carl P. (2011). The Galloping Ghost: The Extraordinary Life of Submarine Legend Eugene Fluckey. Naval Institute Press. p. 91. ISBN 978-1612510460. Retrieved 9 January 2016.