Gokoku Maru was laid down at the Tama shipyard in Okayama Prefecture prior to the outbreak of World War II.
During the building process, she was requisitioned by the Imperial Japanese Navy (in July 1942) and converted into an Armed Merchant Cruiser.
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.
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.