At 04.32 hours on 7 May 1944, U-548 fired two Gnat torpedoes at five ships of the Canadian Escort Group C1 which were returning from escort of convoy ONM-234. HMCS Valleyfield (K 329) (LtCdr D.T. English, RCNR) was hit by one torpedo on the port side in the boiler room, broke in two and sank within four minutes about 50 miles south of Cape Race, Newfoundland. The commander, the senior officer Cdr John Byron (DSC, RD, RNR), ten officers, 111 crew members and two passengers (Lt.(E) John Storey, RCNVR and Surgeon Lt. C.E. Irvine, RCNVR) were lost. 43 survivors were picked up by HMCS Giffard (K 402) (LtCdr Charles Petersen), while HMCS Edmundston (K 106) (LtCdr R.D. Barrett), HMCS Frontenac (K 335) and HMCS Halifax (K 237) carried out an unsuccessful search for the U-boat. Five of the rescued men died on board from exposure, so only two officers and 36 crewmen survived the sinking. The corvette did not immediately pick up survivors as her commander was somewhat indecisive about whether to hunt for the U-boat or risk his ship while being stationary during the rescue. After a short search and the remaining ship realizing what happened, she began rescuing men from the freezing water but by then many had perished further contributing to the disaster.