In the night on 29 May 1940, U-62 proceeded surfaced near the Kwinte Buoy, northwest of Ostend, to attack the ships on the Route Y (Dunkirk - Kwinte Buoy - Ramsgate) during the Allied Operation Dynamo, the evacuation of Allied troops from Dunkirk. At about 02.30 hours, while the U-boat tried to get undetected into an attack position, one of the distant ships detonated in a tremendous explosion and abruptly lit up the night sky. Two torpedoes from the German Schnellboot S-30 (Zimmermann) had struck the ammunition magazine of HMS Wakeful (H 88) (Cdr R.L. Fisher, RN) which disappeared within 15 seconds taking nearly 700 men with her. The fleet minesweepers HMS Gossamer (J 63) (Cdr R.C.V. Ross, RN) and HMS Lydd (J 44) (LtCdr R.C.D. Haig, RN), the British minesweeping drifters HMS Comfort (a former Scottish drifter of 60 tons) and HMS Nautilus (a motor drifter of 64 tons) and the destroyer HMS Grafton (H 89) (Cdr Cecil Edmund Charles Robinson, RN) began picking up the men swimming in the water and lowered lifeboats.

At 02.50 hours, HMS Grafton was hit by one torpedo from U-62 and caught fire. The commander, 15 crew members and 35 troops on deck, just escaped from Dunkirk, were killed by the explosion. The vessels closest to the torpedoed destroyer opened fire on a darkened ship that they believed to have been the attacker - sinking HMS Comfort within minutes by concerted machine gun and cannon fire and ramming by HMS Lydd. At dawn, the burning HMS Grafton was scuttled by three shells from HMS Ivanhoe (D 16) (Cdr P.H. Hadow, RN) about 25 miles northeast of Dunkirk after 130 crew members and approximately 750 troops had been taken off by the British ferry Malines. The survivors were landed at Dover later that day.

Initially the BdU believed that U-62 had sunk the French steam merchant Douaisien (2954 grt) based on reports by the xB-Dienst, but this vessel sank after hitting a mine. Also HMS Nautilus which had picked up survivors from the torpedoed ships was lost off Dunkirk later that day.