"Thornback" had passed her target once at and came about for a second pass when the forward torpedo room reported sharp noises forward. Further amplification showed that the noise was caused by enemy machine gun bullets striking the submarine's hull. Resuming the attack, "Thornback" swung back into action, with visibility only and lessening. Her 40 millimeter fire continued to maul the Japanese vessel, shooting away one of her masts and leaving her limping shoreward at only . After securing from battle stations, "Thornback" passed through an oil slick and noted a mast from the heavily hit patrol craft.