The Blitar (Master W.E. van der Knip) was on station #123 in the convoy HX-231 and left after the first attacks at 01.58 hours on 5 Apr, 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.

At 10.55 hours, U-229 fired a torpedo at the Blitar but missed and opened fire with her deck gun, which was answered by the gunners aboard the vessel. The U-boat broke off the attack due to malfunctions of the gun. After that the ship tried to find the convoy again, but was sighted at about 15.55 hours by U-632. The U-boat followed and fired two torpedoes at 22.39 hours, but both missed. A second attack with two torpedoes failed again.

U-631 (Krüger) also followed the Blitar and fired two FAT torpedoes after the two unsuccessful attacks by the other U-boat but missed too. Thereafter, Karpf signalled Doenitz to ask 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, U-632 fired one torpedo that struck in the engineroom of Blitar, which sank after the boilers exploded.