The third ship of the
Aikoku Maru-class was
Gokoku Maru. Still in the final stages of outfitting when war was declared, she underwent conversion to an armed merchant cruiser while still being completed, and ended up looking markedly different from her sister ships. Commissioned on 25 September 1942, she primarily served as a transport, and was not known to have been sent out on commerce raiding cruises like
Aikoku Maru and
Hokoku Maru. On 19 December 1942, she narrowly escaped being torpedoed by submarine
U.S.S. Albacore; one of the torpedoes meant for her instead struck light cruiser
Tenryu in the stern, mortally wounding her. Rerated a transport on 1 October 1943, she served in this role for the remainder of her life.
On 10 November 1944, she was inbound for Sasebo when she was intercepted by the submarine
U.S.S. Barb, which hit her with two torpedoes, one striking aft of her funnel and the second forward of the bridge. The port engine room was destroyed, the ship flooded, all power was lost, and she took on a 30-degree list to port. Despite this damage, the crew attempts to beach their ship. However,
Barb fired another torpedo, mortally wounding the ship. The last surviving ship of her class,
Gokoku Maru sank stern-first with 326 passengers and crew dead, including her CO, Captain Mizuno Kokichi, who had been in command since the ship was commissioned. Mizuno was posthumously promoted RADM.