Following the conquest of the Philippines in 1942 and the surrender of the United States Army, thousands of Allied prisoners of war, mostly American, were being held on the islands which by 1944 were soon to be invaded by General Douglas MacArthur. To prevent the liberation of the prisoners in the Philippines, the Japanese established a system of transportation called "Hell Ships" by those being transported. These Hell Ships were ordinary merchant vessels used to transport the Allied prisoners from the Philippines to elsewhere in the Japanese empire. These vessels were so-called because prisoners were transported in inhumane and unsanitary conditions amounting to torture. SS "Shinyō Maru" was one of these vessels; displacing 2,634 gross registered tons, she was a tramp cargo steamer impounded by the Japanese in 1941 and crewed by both merchant sailors and Imperial Japanese Army soldiers. The soldiers manned the ship's machine gun and guarded 750 Allied prisoners in the holds, almost 300 of whom were survivors of the Bataan Death March. The Japanese commander is said to have been extremely ruthless. Expecting an attack by the Allies, he told the prisoners that if the ship were fired on, he would order the guards to begin killing them.