Convoy ON 127 Convoy ON - 127 was a trade convoy of merchant ships during the second World War . It was the 127th of the numbered series of ON convoys Outbound from the British Isles to North America and the only North Atlantic trade convoy of 1942 or 1943 where all U - boats deployed against the convoy launched torpedoes . The ships departed Liverpool on 4 September 1942 and were met at noon on 5 September by the Royal Canadian Navy Mid - Ocean Escort Force Group C - 4 consisting of the Canadian River class destroyer " Ottawa " and the Town class destroyer " St . Croix " with the Flower class corvette s " Amherst " , " Arvida " , " Sherbrooke " , and " Celandine " . " St . Croix " s commanding officer , acting Lieutenant Commander A . H . " Dobby " Dobson RCNR , was the senior officer of the escort group . The Canadian ships carried type 286 meter - wavelength radar but none of their sets were operational . " Celandine " carried Type 271 centimeter - wavelength radar . None of the ships carried HF / DF high - frequency direction finding sets . Background . As western Atlantic coastal convoys brought an end to the second happy time , Admiral Karl Dönitz , the " Befehlshaber der U - Boote " ( " BdU " ) or commander in chief of U - Boats , shifted focus to the mid - Atlantic to avoid aircraft patrols . Although convoy routing was less predictable in the mid - ocean , Dönitz anticipated that the increased numbers of U - boats being produced would be able to effectively search the area with the advantage of intelligence gained through " B - Dienst " decryption of British Naval Cypher Number 3 . However , only 20 percent of the 180 trans - Atlantic convoys sailing from the end of July 1942 until the end of April 1943 lost ships to U - boat attack . Initial contact . Wolf pack " Vorwarts " was forming about 500 miles west of Ireland as the convoy left Liverpool . " U - 91 " , " U - 92 " , " U - 96 " , " U - 211 " , " U - 218 " , " U - 380 " , " U - 404 " , " U - 407 " , " U - 411 " , " U - 584 " , " U - 594 " , " U - 608 " , and " U - 659 " formed a search line across the convoy ' s path just beyond the range of land - based aircraft . " U - 584 " reported the convoy on 9 September , but lost contact that evening . 10 September . " U - 96 " regained contact on 10 September and torpedoed the Norwegian tanker " Svene " , the tanker " F . J . Wolfe " and the Belgian freighter " Elisabeth van Belgie " in a single submerged daylight attack . " Sherbrooke " fell back to aid the torpedoed ships while " St . Croix " , " Ottawa " , and " Celandine " searched unsuccessfully for " U - 96 " . " F . J . Wolfe " was able to regain its station with the convoy . " Ottawa " continued to patrol astern of the convoy after " St . Croix " and " Celandine " resumed their normal patrol stations . A coordinated night attack on the convoy began with " U - 659 " torpedoing the British tanker " Empire Oil " on the evening of 10 September . " St . Croix " made SONAR contact immediately prior to the attack and " Celandine " , " Ottawa " , and " St . Croix " searched for " U - 659 " after the attack . " St . Croix " and " Ottawa " fell back to rescue 23 of the stricken tanker ' s crew of 41 . " U - 404 " torpedoed the tanker " Marit II " , " U - 608 " launched torpedoes which missed the convoy , " U - 218 " torpedoed the tanker " Fjordaas " , and " U - 92 " and " U - 594 " launched torpedoes which missed the convoy before " Ottawa " , " St . Croix " , and " Celandine " rejoined the convoy . " Sherbrooke " remained astern of the convoy aiding the ships torpedoed by " U - 96 " , and rescued all but one of the crew of the sinking " Svene " and " Elisabeth van Belgie " . The remaining escorts counter - attacked , and depth charge damage forced " U - 659 " and " U - 218 " to return to port . Both " Marit II " and " Fjordaas " were able to regain their stations in the convoy . " Empire Oil " was later sunk astern of the convoy by " U - 584 " . 11 September . None of the escorts ' RADAR sets were functional on 11 September . " U - 584 " torpedoed the Norwegian " Hindanger " in a submerged daylight attack while " St . Croix " investigated a visual sighting six miles distant . " Amherst " fell back and rescued all but one of " Hindanger " s crew . A B - 24 Liberator patrol bomber of No . 120 Squadron RAF prevented further daylight attacks on 11 September but " U - 96 " sank a 415 - ton Portuguese sailing trawler by gunfire in the vicinity of the convoy . In coordinated night attacks , " U - 380 " missed with a salvo of four torpedoes , " U - 211 " torpedoed the British whale factory ship " Hektoria " and freighter " Empire Moonbeam " , " U - 92 " missed " Ottawa " with four torpedoes and " U - 404 " torpedoed the tanker " Daghild " before " Amherst " and " Sherbrooke " rejoined the convoy . " Daghild " maintained station in the convoy and " Arvida " rescued all but four of the 140 crewmen from " Hektoria " and " Empire Moonbeam " before those ships were sunk astern of the convoy by " U - 608 " . Parting shots . Excellent visibility on 12 September allowed a close forward screen of four escorts to discourage U - boats sighted up to 7 miles away . " U - 407 " and " U - 594 " launched torpedoes unsuccessfully that night . " U - 594 " sank the straggling " Stone Street " as the convoy came within range of Canadian Canso patrol bombers from Botland , Newfoundland on 13 September . The escort was reinforced at dusk by the Town class destroyer HMCS " Annapolis " and the V and W class destroyer HMS " Witch " from the Newfoundland - based Western Local Escort Force ( WLEF ) . Both " U - 91 " and " U - 411 " launched torpedoes unsuccessfully while " U - 91 " torpedoed the Canadian River class destroyer " Ottawa " in the pre - dawn hours of 14 September . " Ottawa " sank with 114 of its crew . The remainder of the convoy reached New York City on 20 September 1942 .