to the 9th U-boat Flotilla. France U-377 sailed from Brest on 15 April, out into the mid-Atlantic, and patrolled for 54 days, before returning to base on 7 June. On 2 August 1943 her commander, Otto Köhler, left the boat and was replaced by Oberleutnant zur See Gerhard Kluth. Kluth's first patrol was quite eventful, as her first two attempts were cut short; U-377 sailed from Brest on 26 August 1943, but returned on the 30th; she sailed again on 6 September 1943, returning the next day. Finally she set out again on 9 September, joining other U-boats in mid-Atlantic. On 22 September, the U-boat was attacked by a B-24 Liberator, wounding the commander. The U-boat returned to port under the command of the I WO. Leutnant zur See Ernst-August Gerke. Loss U-377 departed from Brest on 15 December 1943, with Kluth back in command, sailing out into mid-Atlantic. She made her last radio report on 15 January 1944, claiming to have attacked an unidentified search group with homing torpedoes. The BdU ("U-boat Command") expected the U-boat to head back to France on or about 29 January, so when she had failed to arrive by 10 February, she was listed as missing from 4 February 1944. After the war the Allied Assessment Committee were unable to attribute the loss of U-377 to any known anti-submarine attack, and the U-boat was officially recorded as "lost to unknown cause". The Kriegsmarine had received at least two partially corrupted unsigned coded emergency messages around the time of the U-boat's disappearance, leading to a theory that U-377 had been sunk by one of its own Zaunkoenig T-5 acoustic torpedoes. This explanation has been generally accepted post-war. However, an attack by the British destroyer and frigate at , on 17 January took place two days and about from U-377s last known position (where she would have been, had she been on course and sailing at the most economical speed, as ordered) and recent research suggests that this was the U-boat's fate. Wolfpacks U-377 took part in 15 wolfpacks, namely: Aufnahme (7 – 11 March 1942) Blücher (11 – 18 March 1942) Bums (6 – 14 April 1942) Blutrausch (15 – 17 April 1942) Trägertod (12 – 21 September 1942) Ritter (11 – 21 February 1943) Neptun (22 February – 2 March 1943) Amsel (22 April – 3 May 1943) Amsel 2 (3 – 6 May