On 29 June 1944, Toyama Maru was transporting over 6,000 men of the Japanese 44th Independent Mixed Brigade when she was torpedoed and sunk.

In 1943 As the result of a merger, Toyama Maru is transferred to Taiyo Kogyo, K. K. She would continue to serve as a Troop transport until June 1944.

[2] On 27 June 1944, Toyama Maru departed Kagoshima Bay bound for Naha City on what would become her final voyage, with over 6,000 men aboard.

At 07:30, the American submarine USS Sturgeon (SS-187), stalking the convoy, spotted and fired four torpedoes at Toyama Maru.

A third torpedo hit mid-ship, breaking the ship in half and she promptly sank in the Nansei Shoto, off Taira Jima, Japan, at approximate position 27º47'N, 129º05'E.