 In December 1942, "Onslow" took part in Arctic Convoy JW 51B, joining the convoy on 25 December, with Captain Robert Sherbrooke taking charge of the convoy's close escort of six destroyers, two corvettes, one minesweeper and two trawlers.Five merchant ships, together with the destroyer "Oribi" and one of the trawlers, were separated from the convoy by bad weather shortly afterwards.On 30 December, the convoy was spotted by the German submarine , and in response a German force consisting of the heavy cruisers "Lützow" and and six destroyers set out from Altafjord to intercept the convoy.