At 03.11 hours on 12 Aug 1941, U-568 fired torpedoes at convoy ON-4 south of Iceland, observed a hit on a corvette and heard another detonation. Preuss assumed that he had probably damaged a tanker in convoy but this was not the case. HMS Picotee (K 63) (Lt R.A. Harrison, RNR) was hit by the torpedo underneath the bridge, broke in two and sank immediately, while her own depth charges detonated. The commander, four officers and 61 ratings were lost. The corvette of the 4th Escort Group was reported missing after she did not return to convoy from a search for a reported U-boat.