At 09.04 hours on 24 June 1942, U-156 began shelling the unescorted Willimantic (Master Leon Otto Everett) about 700 miles southeast of Bermuda. The ship had been sighted and reported by U-502 (Rosenstiel) the day before. At 16.10 hours on 23 June, U-156 made contact, followed the zigzagging ship and at 08.10 hours fired her last torpedo, which became a tube runner and missed behind the ship after being pushed out. The shelling killed both radio officers in the radio room and two crewmen when both starboard lifeboats were destroyed. The Germans ceased fire to question the survivors, apologized for the casualties, provided some charts and took the master as prisoner on board. At 10.52 hours, the U-boat reopened fire until the ship sank at 11.45 hours after spending 73 rounds for the deck gun and 102 rounds for the 37mm AA gun. In all, six crew members were lost. The master was landed at Lorient on 7 July and taken to the POW camp Marlag und Milag Nord. 14 crew members and two gunners in one lifeboat were picked up after six days by the Norwegian motor merchant Tamerlane and landed at Rio de Janerio. 14 crew members and one gunner in another lifeboat made landfall after twelve days at St. Martin’s Island, Lesser Antilles and were taken by the Dutch steam merchant Baralt to St. Thomas, Virgin Islands.

The master Leon Otto Everett had already experienced two other sinkings when Bonheur was sunk by U-138 (Lüth) on 15 Oct 1940 and Swinburne by a German Fw200 aircraft of KG 40 west of Ireland on 26 February 1941.