At 09.42 hours on 27 June 1943 the unescorted Sebastian Cermeno (Master David Martin Nilsson) was hit on the port side by two torpedoes from U-511 about 290 miles southeast of Madagascar. The torpedoes struck the after part of the #5 hold and the forward part of the #4 hold and blew off the after two hatches, destroyed the quarters of the armed guards, buckled the gun deck, disabled the engines and killed one officer and two men on watch below. A sailor who had been asleep on the #4 hatch later died of injuries. The survivors among the eight officers, 34 crewmen, 27 armed guards (the ship was armed with one 5in, one 3in and eight 20mm guns) and five passengers on board abandoned ship in five lifeboats after five minutes. Ten minutes after the hits, the ship sank quickly by the stern. Then the U-boat surfaced and questioned the survivors before leaving the area.

The radio had been smashed by the first torpedo but distress signals were sent daily from an emergency transmitter in one of the lifeboats. The boats became separated during the first night. On 14 July, the 19 survivors in the boat of the master were picked up by the American steam merchant Theodore Parker and landed at Durban the same day. The men in the second boat were picked up by a British corvette and landed at Durban on 23 July, while the 11 survivors in another boat were picked up by an Australian destroyer and landed in Durban on 27 July after being spotted by a patrol aircraft. One boat with 16 survivors made landfall in Madagascar on 5 July and the last was towed into Durban by an Allied ship after 16 days at sea. The first engineer died of exposure in one of the lifeboats on 13 July and was buried at sea.

The master David Martin Nilsson took over the command of another Liberty ship, the Jean Nicolet, which was sunk by the Japanese submarine I-8 (Ariizumi) in the Indian Ocean on 2 July 1944. The most of the survivors from the ship were massacred by the Japanese crew and the master was taken prisoner but did not survive the captivity.