At 09.10 and 09.14 hours on 21 Sep 1943, U-593 fired two spreads of two torpedoes at convoy NSS-3 about 45 miles south of Salerno, heard one detonation from the first and observed one hit from the second spread and reported one freighter probably sunk and another damaged. However, only the William W. Gerhard (Master Olof J. Anderson) in station #13 was hit by one torpedo on the port side in the middle of the #1 hold. The explosion lifted the bow up, broke steam and water lines and buckled the deck. As the ship settled by the bow, a large crack appeared on both sides and caused the flooding of #3 hold. The eight officers, 38 crewmen, 30 armed guards (the ship was armed with one 5in, one 3in and eight 20mm guns) and 191 passengers (US and British Army personnel) abandoned ship in four lifeboats, four rafts and 15 floats. The crew was ordered by the escort commander to reboard the vessel and to stand by for a tow. The remaining survivors were picked up by the escort vessels and taken to Salerno on 22 September. One armed guard was killed by the explosion and another died of wounds aboard the British hospital ship HMHS Vita on 23 September. Three crew members and six armed guards were injured and hospitalized.

At 13.00 hours, the William W. Gerhard was taken in tow by USS Moreno (ATF 87), but three hours later a fire broke out in #1 hold and the tug took off the crew. Assisted by USS Narragansett (ATF 88) and HMS Weazel (W 120) the fires were fought for two hours, but it went out of control and ignited the cargo of ammunition at 21.40 hours. The explosions broke the vessel in two, the forward part sank immediately and the after part was scuttled by gunfire from the tugs at 10.55 hours on 22 September.