Having not been sunk, as had been believed by the Allies, "U-171" continued its patrol. On 13 August 1942 it sank the 6,779-ton US tanker "R. M. Parker Jr." at which is about south of Isles Dernieres, Louisiana. The ship, which was carrying water ballast, was struck by two torpedoes; the submarine then surfaced and fired five rounds from its deck gun into the wreck. The whole crew of 44 survived, being picked up eight hours later by the United States Coast Guard auxiliary .