At 07.18 hours on 2 June 1942 U-553 fired a spread of two G7e torpedoes and after a running time of 123 seconds one of them hit the unescorted Mattawin (Master Charles Herbert Sweeny), which was steaming on a non-evasive course at 9.75 knots in a very dark night and fine weather about 190 miles east-southeast of Nantucket Island. The U-boat had first spotted the ship three and a half hours earlier and already carried out an unsuccessful attack with a spread of two torpedoes at 05.48 hours, but one malfunctioned and the other was a dud. The ship was struck on port side in the bow and stopped after turning hard to starboard. The violent explosion blew away the forefoot and the starboard anchor, threw up a huge column of water and lifted the forecastle head deck, jamming the doors and making it very difficult for some of the men to get out. One sailor on lookout on the forecastle was blown into the water, he was later rescued by one of the lifeboats that were subsequently launched. Most of the 52 crew members, seven gunners (the ship was armed with one 4in gun, one 20mm and eight machine guns) and twelve passengers (American Field Service personnel) aboard abandoned ship in the four boats when she settled by the head and it appeared that the collision bulkhead had collapsed. Only the master, chief and second officer, an apprentice and the carpenter were still aboard when the U-boat fired one G7a torpedo as coup de grâce at 07.30 hours, which struck on port side abaft the engine room in #4 hold. Those men still aboard either jumped overboard or went into #1 boat, which got fouled and just managed to push clear as the ship sank. Ammunition in #4 twin decks and large quantities of oil drums stowed adjacent probably contributed to the force of the second torpedo hit and caused the Mattawin to sink vertically by the stern with a broken back and a list to starboard in about 5 minutes. Having already identified their victim from a distress signal that had been send after the first torpedo hit, the Germans did not question the survivors and left the area.

All lifeboats had modern equipment and food supplies, including pemmican, chocolate, chewing gum, salted peanuts and 36 gallons of water in each one. None had been damaged and all were lowered quickly, everyone behaved very well and there was no sign of panic or confusion, even the chronometer and sextant of the master had been recovered by a sailor. 15 men were in #1 boat in charge of the master, 17 were in chief officer’s boat, 19 in the third officer’s boat and 20 in the motor launch, which was in charge of the second engineer as the second officer had been forced to leave in #1 boat, but it was too risky to transfer him due to a nasty choppy sea. Not knowing if their distress signal had been received ashore they used the emergency set in one of the boats to send further messages in regular intervals. At daylight the lifeboats set sail after a compass comparison, steering northwest to make Cape Cod with a good breeze from the starboard quarter, all four boats keeping together in line ahead and the master reckoned on making land in about seven days. That afternoon the boat of the third officer began to fall astern and the master ordered the motor launch to steam ahead and try to find a rescue ship after the second engineer repaired its engine. He had found it inoperable as it was soaked with water, so he organized pumping parties to bail the boat out, dried the magneto, used massage oil from the lifesaving equipment to lubricate the crank bed and got the engine working perfectly. The senior radio officer and one of the American passengers, with a good deal of experience in motor yachts, helped the engineer officer to navigate.

During the next night the wind dropped and about midnight there was a heavy rain followed by a light breeze. At daylight on 3 June the master could only see the chief officer’s boat on their port bow. Meanwhile the motor launch was sighted by the Torvanger (Master Leif Danielsen) which went alongside, but the occupants told the master that they did not wish to leave their boat after learning that she was bound for Capetown and reported there were three more lifeboats not far away. They were quite sure to reach land safely, so the Norwegians gave them some more petrol and proceeded. Shortly thereafter Torvanger encountered the chief officer’s boat, but they too wished to proceed after only 15 minutes alongside, so the Norwegian ship headed towards the nearby lifeboat with the master of Mattawin, who also declined to be taken aboard and only took some bread and cigarettes when supplies were offered. However, soon after this boat left the master of Torvanger hailed it to return alongside and told them that his officers and crew had insisted on picking up the survivors and returning to New York, as they did not wish to proceed without an escort after already having rescued survivors from two other ships sunk by U-boats – the Polyphemus and Norland – in less than 48 hours. So the Torvanger picked up the master, 22 crew members, four gunners and five passengers from the two closest lifeboats, which were also hoisted aboard and then tried to locate the motor launch again, but it became very hazy. The survivors only asked to be taken to Cape Cod, where they would land in their own boats, owing to engine trouble the Norwegian master decided to go into Halifax. At noon on 4 June the ship met convoy BX-22 en route from Boston to Halifax and kept ahead of it until reaching the harbor later that day, where the survivors were landed together with their lifeboats. Torvanger made repairs and continued her voyage to Capetown two weeks later, but did reach her destination as she was sunk by U-84 (Horst Uphoff) west of the Azores on 23 June.

The 14 crew members, two gunners and four passengers in the lifeboat in charge of the second engineer made landfall at Nauset Beach, Massachusetts and were taken to Eastham on 5 June. USCGC General Greene (WPC 140) picked up the 15 crew members, one gunner and three passengers in the third officer’s boat, brought them first to Nantucket, Massachusetts on 7 June and then to Newport, Rhode Island the next day. One crew member had been injured during the sinking and two had swollen feet by exposure in lifeboat, so they were taken to the US Marine Hospital at Brighton, Massachusetts.