The Blitar (Master Willem Egbert Knip) was in station #123 of convoy HX-231 and left after the first attacks at 01.58 hours on 5 April 1943, because the master decided he had a better chance of making it to the UK on his own. The Thomas Sumpter and the Vaalaren followed. Only Thomas Sumpter arrived in the UK, the other ship was sunk with all hands by U-229 (Schetelig) at 05.09 hours the same day. A few hours later this U-boat also spotted the unescorted Blitar about 420 miles east-southeast of Cape Farewell, overtook the ship that proceeded at 12.5 knots and fired one torpedo at 14.55 hours, but missed due to her zigzag course. Schetelig realized that they were unable to overtake the fast ship again as the U-boat was very low on fuel and attempted to stop the Blitar in position 56°46N/30°45W by opening fire with the deck gun after surfacing two miles astern of her at 15.10 hours. However, after firing six rounds the gun was jammed by an empty shell stuck in the breech. All shots fell short and also eight rounds fired by the Blitar from her 4in gun aft did not reach the U-boat, which dived after the inconclusive gun duel that only lasted 5 minutes and left the area to refuel from the tanker U-462 (Vowe).

Shortly thereafter the Blitar was spotted by U-632 (Karpf) at about 15.55 hours. The U-boat began to chase the ship and was joined by U-631 (Krüger) after about four hours, but the latter remained on distance when they observed how the other U-boat dived for a submerged attack at 20.46 hours. Karpf reported that he had missed with a spread of two torpedoes at 22.39 hours, so Krüger fired two FAT torpedoes at 00.03 hours on 6 April that missed like the two FAT torpedoes fired by U-632 at 00.10 hours. Thereupon Karpf sent a radio message to ask the BdU which U-boat was allowed to attack and he was granted to sink the ship because he was older.

At 01.36 hours on 6 April the Blitar was struck on starboard side in the engine room by one torpedo from U-632 about 520 miles east of Cape Farewell. The ship stopped, began to settle on an even keel and the crew of 72 men and eight British gunners (the ship was armed with one 4in, two 20mm and three machine guns) abandoned ship in the three port lifeboats because those on starboard had been destroyed. No distress signals could be sent. After they were clear of the ship, another torpedo hit in #3 hold that caused a huge flame and a slight list to port. Blitar sank vertically by the bow after being hit by a third torpedo and about 30 minutes after the first torpedo hit. 21 crew members were lost.

U-631 had witnessed the sinking and then approached one of the lifeboats to question the survivors, but due to rough seas in a fresh breeze the boat #2 could not get alongside so one of the survivors was ordered to jump into the water and swim to the U-boat. This was done by the master, but he had discarded his uniform and all other marks of identification and succeeded in letting the Germans believe that he was just a sailor and that all officers had been lost in the sinking. The only information he disclosed during a short interrogation was that the ship was en route to the UK with a cargo of hides, not even stating its name or port of destination. Krüger decided to not keep him as prisoner aboard because the U-boat would remain on patrol for several weeks, so he was allowed to return to the lifeboat. However, the master apparently drowned on his way back, probably because he had already been exhausted from swimming to the U-boat.

This left the lifeboat #2 with 27 occupants in charge of the chief officer, but four survivors died during the night and were buried at sea. At dawn the lifeboat #4 with 15 occupants was spotted and they remained together while sailing towards Ireland. The next day they were spotted by a patrol aircraft in position 56°02N/22°35W which dropped three packages with provisions. On 10 April, the survivors attracted the attention of the escorts of convoy ON-177 in position 59°03N/19°05W by firing flares and the 23 men in boat #2 were picked up by HMCS Restigouche (H 00) (LtCdr D.W. Piers, RCN) at 08.30 hours, while the 15 men in boat #4 were picked up by HMS Trent (K 243) (LtCdr J.G. Rankin, DSC, RNR) two hours later. They were all landed at St. John’s, Newfoundland on 18 April. Lifeboat #6 was in charge of the second officer with 16 occupants and lost contact with the other boats during the first night, but also set sail to Ireland at dawn. On 8 April, their boat was sighted by a Sunderland flying boat that dropped food rations and directed HMS Eclipse (H 08) (LtCdr E. Mack, DSO, DSC, RN) from convoy HX-231 to them. They were picked up at dawn in position 56°06N/22°20W and landed in Reykjavik, Iceland on 10 April.