At 08.18 hours on 30 August 1942 the unescorted Jack Carnes (Master Theodore Roosevelt Merritt) was attacked by U-705 (Horn) with a spread of four torpedoes in 45°35N/28°02W, while steaming a zigzag course at 14.5 knots. One detonation with a smoke cloud was observed by the U-boat, but the tanker was not hit. The U-boat then surfaced and began shelling the ship from a distance of about five miles. About ten shots were fired and none struck the ship, but shrapnel was scattered over the deck. The armed guards fired eight rounds from the forward 3in gun and 13 rounds from the after 4in gun (the ship was also armed with four 20mm and two .30cal guns), forcing the U-boat to submerge.

At 01.54 hours on 31 August 1942 the Jack Carnes was attacked by U-516 with a spread of two torpedoes of which one struck on the starboard side forward of the bridge. The master ordered the helm to be swung to starboard, but the watch below erroneously secured the undamaged engines and the ship lost way. Four minutes after the first hit, the U-boat fired a torpedo which struck on the port side in the #4 tank, followed by a coup de grâce which struck the starboard side amidships. The nine officers, 33 crewmen and 14 armed guards then abandoned ship in two lifeboats. A fifth torpedo was then fired by the U-boat, which struck the starboard side aft of the midships house, a sixth hit the starboard side bunker tanks and a seventh struck amidships. After the last hit, the tanker broke in two and sank, bow rising into the air at 04.26 hours.

The survivors set sail together in a southerly direction, but a storm during the night reached gale force and separated the boats. Six days later, the boat with the chief mate, four other officers, 19 crewmen and four armed guards made landfall on Terceira Island, Azores. They were first taken from Angra to Ponta Delgada by the Portuguese destroyer Tejo on 8 September, then landed at Horta by the Portuguese steam merchant Carvalho Araujo on 29 September from where they were eventually repatriated aboard two Clipper flying boats. The other boat containing the master, three other officers, 15 crewmen, eight armed guards and two British gunners was never seen again.