Norway

U-377 sailed from Kiel on 14 February 1942 and patrolled along the coast of Norway before arriving at Narvik on 28 February.^[5] This was her home port for the rest of the year, she sailed on a series of six patrols in the Barents Sea, without success.^[2]

On 30 January 1943 U-377 left Bergen and sailed out into the Atlantic, patrolling south of Greenland, before arriving at Brest in France on 18 March, having been transferred to the 9th U-boat Flotilla.^[6]

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.^[7]

On 2 August 1943 her commander, Otto Köhler, left the boat and was replaced by Oberleutnant zur See Gerhard Kluth.^[1] 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,^[2] 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.^[1]

Loss

U-377 departed from Brest on 15 December 1943, with Kluth back in command, sailing out into mid-Atlantic.^[8] 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.^[9][10] However, an attack by the British destroyer HMS Wanderer and frigate HMS Glenarm at 49°39′N 20°10′W, on 17 January took place two days and about 220 nautical miles (410 km; 250 mi) from U-377's 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.^[11]

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 1943)
• Elbe (7 – 10 May 1943)
• Elbe 2 (10 – 14 May 1943)
• Leuthen (15 – 22 September 1943)
• Borkum (24 December 1943 – 3 January 1944)
• Borkum 3 (3 – 13 January 1944)
• Rügen (13 – 17 January 1944)