Three days later, by periscope, the submarine spotted a 950-ton "sea truck", similar to "Sanko Maru", at , close inshore. Unescorted, the Japanese presented a tempting target for a gun attack, but, no sooner had "Thornback"’s periscope shears and bow broken the surface, than the target slipped into the misty weather. Not to be daunted, "Thornback" followed, playing a cat and mouse game, and fired five torpedoes. All missed. She later sighted the enemy again, missed with three more torpedoes, and took the "sea truck" under fire. Despite poor visibility, "Thornback" closed to and scored numerous hits with the 40 millimeter guns. The target, however, was able to move closer inshore and escaped in the fog which closed around her like a shroud.