 There, she sank the British vessel "Wanstead" south of Greenland, whose survivors were picked up by the corvette and the ASW (anti-submarine warfare) .Her fourth sortie was a frustrating one; it was split into three parts, but she failed to sink any ships.On 20 February 1944, she sank the British 1,100 ton destroyer about 15 miles off Trevose Head, north Cornwall.