Between 02.43 and 02.46 hours on 5 May 1943, U-628 fired six torpedoes at convoy ONS-5 about 500 miles south of Cape Farewell and reported one ship sunk, one ship probably sunk, one ship burning and two end-of-run detonations. However, only the Harbury (Master Walter Edward Cook) was hit. Six crew members and one gunner were lost. The master, 33 crew members and eight gunners were picked up by HMS Northern Spray (FY 129) (Lt F.A.J. Downer) and landed at St.Johns. It is possible that Hasenschar thought that the ships sunk by U-264 (Looks) at the same time were his own victims.
At 05.02 hours, U-628 fired her last torpedo against a corvette and observed a huge tongue of flame after 28 seconds and a heavy explosion afterwards, the target disintegrating. However, Allied sources do not report the loss of any escort vessel.
At 16.51 hours, U-628 finished off the wreck of the Harbury with 40 rounds of 8.8cm and 100 rounds of 2cm gunfire. The vessel capsized to starboard at 17.37 hours and sank in 55°10N/42°58W (grid AJ 6453).