'Isegrim' was a U-boat wolfpack operation in the Arctic against the JW.56A and JW.56B convoys (20/27 January 1944).

The wolfpack comprised U-278, U-312, U-314, U-360, U-425, U-472, U-601, U-636, U-716, U-737, U-739, U-956, U-957 and U-965, and for the loss of none of its own number sank three ships (14,431 tons), and also damaged the British destroyer Obdurate.

On 12 January the JW.56A convoy departed Loch Ewe on the west coast of Scotland with 20 laden ships and the local escort of the destroyer Inconstant, the sloop Cygnet, the corvettes Borage, Dianella and Poppy, and the minesweepers Orestes and Ready. The convoy ran into a storm on 16 January and took shelter at Akureyri in northern Iceland. Five ships had to remain there with storm damage, but on 21 January the rest of the convoy again put to sea with 15 ships supported by Captain W. G. A. Robson’s escort group (frigate Hardy, destroyers Savage, Venus, Offa, Obdurate, Inconstant, Vigilant, Virago and Free Norwegian Stord, corvettes Poppy and Dianella, and minesweepers Ready and Orestes). Vice Admiral A. F. E. Palliser’s covering force comprised the heavy cruisers Kent and Norfolk, and the light cruiser Belfast.

On 22 January Loch Ewe was also the starting point for the JW.56B convoy, with 17 laden ships, of which one soon turned back, supported by Captain I. M. R. Campbell’s escort group comprising the destroyers Milne, Musketeer, Opportune, Mahratta, Scourge, Canadian Huron and, later, Meteor. The close escort comprised the destroyers Westcott, Whitehall and Wrestler, the sloop Cygnet, the corvettes Honeysuckle, Oxlip and Rhododendron, and the minesweepers Onyx, Hydra and Seagull. Cruiser cover was provided by the heavy cruisers Berwick and Kent, and the light cruiser Bermuda.

As a result of reports from agents in Iceland, Kapitän Hans Rudolf Peters, the Führer der Unterseeboote 'Norwegen', ordered the establishment of the 'Isegrim' wolfpack with 10 boats in the Bjørnøya Passage. Although German air reconnaissance failed to spot the convoy, with the exception of the most northerly U-739 the wolfpack’s boats arrived from about 12.00 on 25 January and attacked in the dark hours of the afternoon and night of 25/26 January. U-965, U-601, U-360 (four times), U-425 (twice), U-737, U-278 and U-314 fired torpedoes at the convoy’s escorts but hit only Obdurate, which was merely damaged by a weapon from Kapitänleutnant Klaus-Helmuth Becker’s U-360. Kapitänleutnant Joachim Franze’s U-278, Becker’s U-360 and Oberleutnant Hans Dunkelberg’s U-716 successively fired torpedo salvoes at the convoy and hit the 7,177-ton US Penelope Barker, 7,153-ton British Fort Bellingham and 7,200-ton US Andrew G. Curtin respectively. All three ships sank, Fort Bellingham being finished by Oberleutnant Gerd Schaar’s U-957, which rescued survivors.

On 26 January the Soviet destroyers Gremyashchiy, Gromkiy and Razyarennyi, the British minesweepers Gleaner and Speedwell, and the Soviet minesweepers T-111, T-114 and T-117 met the convoy, which entered the Kola inlet on 28 January. Seven transports and two tankers then passed with a Soviet escort to the White Sea and Arkhangyel’sk. Robson met the JW.56B convoy with six destroyers to strengthen the anti-submarine defences.

After ordering an end to operations against the JW.56A convoy, Grossadmiral Karl Dönitz, commander-in-chief of the German navy but still in day-to-day operational control of the U-boat arm via Konteradmiral Eberhard Rodt, the U-boat arm’s operational commander, mandated the re-establishment of the 'Werwolf' (i) wolfpack in a form reinforced with U-313, U-472, U-956, U-973 and U-990, in the Bjørnøya Passage to operate against the next convoy. This was the JW.56B convoy, which was reported at mid-day on 29 January by U-956. By the morning of 30 January U-737, U-601 (twice), U-957 (four times), U-278, U-472, U-425 (twice) and U-313 had launched torpedoes against the escort vessels, but only Franze’s U-278 achieved any success when one of its weapons struck Hardy, which had to be sunk by Venus. U-737 and U-957 missed Milne and Stord only by narrow margins. Kapitänleutnant Georg-Wilhelm Basse’s U-314 was sunk by the destroyers Whitehall and Meteor, and no boat achieved a firing position against the merchant ships.

Up to a time early on 31 January, U-965, U-425 (twice), U-737, U-956 and U-990 also fired unsuccessful torpedoes against the escorts. On 1 February a Soviet escort group with the destroyers Gremyashchiy, Groznyi and Razyarennyi, the British minesweeper Gleaner, the Soviet minesweepers T-111 and T-117, and two submarine chasers rendezvoused with the convoy and escorted seven of its number to the White Sea.

U-956 also fired torpedoes during its return journey on 1 February, the day the convoy’s 16 ships entered the Kola inlet.