The destroyers HMS Fortune and HMS Faulknor (who sank U-39 six days earlier), had been part of a concerted effort to find and sink the U-Boat that had been attacking trawlers. On 20 September 1939, three torpedoes were fired at the warships, but failed to do any damage when they exploded prematurely. The British vessels replied with a series of depth charge attacks, one of which damaged the German submarine sufficiently to force it to the surface.