The alerted destroyer made several runs over D4, which was submerged in water only 30 feet (9.1 metres) deep, in an attempt to ram her, but did not succeed and eventually left the scene.

Although the Germans salvaged Bielefeld, she did not go back into naval service and instead was returned to her pre-war civilian owners.

At 04:30 that day, whilst on patrol approximately midway between Guernsey and Portland Bill, D4 observed UB-72 on the surface travelling in a southerly direction some two miles distant.

Five minutes later Lt Claud Barry, in command of D4, saw UB-72, obviously unaware of the British boat's presence, alter course so that the U-boat appeared to be approaching D4.

At 0450 Lt Barry fired a torpedo 600 yards (550 metres) from the target and after lowering the periscope for a few moments he released a second one.