Tamatsu Maru was a World War II Japanese landing craft depot ship^[2] completed in January 1944^[3] and remembered for the heavy loss of life when sunk by USS Spadefish^[2] on 19 August 1944. Between 4,406 and 4,755 Japanese soldiers and seamen drowned.^[4]

Tamatsu Maru was laid down at Mitsui Shipbuilding on 4 November 1942, launched on 18 August 1943, and completed on 20 January 1944. Its first military loading was from Moji to Manila with convoy Hi-45 in February 1944. It returned to Japan in March to transport elements of the 30th Infantry Division of the Imperial Japanese Army (IJA) from Pusan to the Philippines with convoy Hi-63 in May. It returned to Japan with convoy Hi-62 in early June to transport the IJA 5th Field Heavy Artillery and 58th Independent Mixed Brigade to the Philippines with convoy MOMA-01 in July. It returned to Japan in early August with convoy Hi-68.^[3]

Tamatsu Maru departed Pusan on 8 August 1944 carrying the Japanese 2nd Battalion and regimental headquarters of the 13th Independent Infantry Regiment from Korea for defense of the Philippines. It joined convoy Hi-71 departing Moji on 10 August, and stopping at the Mako naval base in the Pescadores on 15 August. Convoy Hi-71 departed Mako on 17 August^[3] and was discovered by USS Redfish that evening. Redfish assembled other submarines for a radar-guided wolfpack attack on the evening of 18 August in heavy rain.^[5]

As the convoy was scattered by heavy seas and evasive maneuvers, Tamatsu Maru apparently became separated from convoy escorts. Spadefish found Tamatsu Maru on a northerly course^[5] about 0330 19 August and fired a salvo of six torpedoes. Spadefish heard two torpedoes hit. Convoy escorts were unaware of the ship's location (17°34′N 119°24′E) until one of them discovered thousands of floating bodies that afternoon.^[3] The sinking of Tamatsu Maru was the fourth worst loss of life on any Japanese vessel during the war taking down 4,755 troops and 135 merchant seamen.^[6]

• List by death toll of ships sunk by submarines