At 09.26 hours on 7 Oct, 1942, the unescorted Firethorn (Master Paul F. Schultz) was hit by two torpedoes from U-172 about 60 miles northwest of Capetown. The first torpedo struck on the port side just below the bridge, tearing open the hull. The second struck in the engine room a few seconds later, causing the ship to sink within two minutes with a heavy list to port. No lifeboats were launched and the 40 crew members and 21 armed guards abandoned ship in four rafts and a yawl boat, which floated free. The Danish master, nine crew members and two armed guards died. The yawl boat was found bottom up, was rightened and used to pick up the men swimming in the water and place them on the rafts which were eventually lashed together. Six men in the yawl boat set forth for the coast. They were spotted by an aircraft the next day and were picked up four hours later by the HMS Rockrose (K 51) (Lt E.J. Binfield, RNR). On 9 October, the remaining survivors were picked up by the same corvette and a minesweeper and taken to Capetown, arriving the same day.

Six armed guards and two crewmen from Firethorn were lost during repatriation on Zaandam, which was sunk by U-174 (Thilo) on 2 November. One crew member from Firethorn survived 82 days on a raft together with two survivors from the Dutch ship.