Commanded by Lieutenant Commander The Hon. Byron Plantagenet Cary, Bt., "G9" had sailed Scapa Flow on 9 September to patrol an area between Shetland and Norway. On 15 September, she was ordered north to between latitudes 60.30 N and 61.30 N to keep her clear of the fleet on exercises en route from Rosyth to Scapa. Meanwhile, "Pasley" was attempting to locate merchantmen detached from the convoy she was escorting in appalling weather from Russia via Aspö Fjord, 100  km north of Bergen, to Lerwick, and had resorted to displaying a white light halfway up the mast by night for guidance. Weathering the heavy seas and blinding rain squalls, Cary sighted "Pasley"'s light; forewarned a U-boat was in the area, he gave the order to attack. Presumably realizing the error soon afterwards, Cary ordered the connection of the cruiser arc lamp to signal the destroyer. The signal was recognised aboard "Pasley"; her captain, Commander Charles Ramsey, ordered 'Full Astern', but it was too late to prevent his ship ramming the submarine.