At 04.16 hours on 21 Nov 1942, U-518 fired a spread of two stern torpedoes at two overlapping steamers in convoy ON-145, at 04.24 hours one single bow torpedo at a special ship and one minute later a spread of two bow torpedoes at one of the biggest ships about 200 miles southeast of Sydney, Nova Scotia. Wissmann could not observe the results as he was forced to crash dive after the attack, but heard three detonations and claimed the sinking of two ships. In fact, the British Promise in station #61, the British Renown in station #71 and the Empire Sailor in station #82 had been hit by one torpedo each.

The Empire Sailor (Master Fred Wilkinson Fairley) had originally been in station #92, but convoy was reduced from nine to eight columns after the southbound ships were detached on 18 November, so her station was altered to #82 as the second ship of the outer starboard column. Only the senior officers aboard were aware of the dangerous cargo the ship carried in #4 hold, a deep tank abaft the engine room, which had been specially sealed and fitted with ventilating pipes as it contained 270 tons of phosgene gas in cylinders for use in 5” rocket shells and #1 hold contained 60 tons of mustard gas in drums and 100 tons of commercial cyanide. Her lookouts had just witnessed the torpedo hits on the two tankers ahead when one torpedo struck on the port side directly in #4 hold while steaming at 9.5 knots in fine and clear weather with a moderate swell. The explosion blew the hatches and beams off #4 and #5 holds and with them six cylinders of phosgene fell back on deck abaft the bridge, releasing the poisonous gas. The engineers on watch stopped the engines and the master immediately gave the order to abandon ship. There were 53 crew members, five gunners (the ship was armed with one 4in, one 12pdr, four machine guns and three depth charges) and five passengers (two Canadian signalmen and three Canadian Army personnel to look after the poison gas) aboard and all except three missing crewmen left within eight minutes in all four lifeboats, although one of them had been damaged by the explosion. No distress signals were sent but an emergency set was lowered into one of the boats. The chief officer threw five weighted bags of diplomatic mail overboard that were addressed to the Admiralty in Ottawa and made sure that the other 33 bags were locked in a passenger’s room before leaving the ship, which took a list of 15° to port. Less than one hour later, HMCS Minas (J 165) (T/Lt W.F. Wood, RCNR) arrived and picked up the master and the occupants of three lifeboats but was then ordered to rejoin convoy so the 17 men in the fourth lifeboat in charge of the chief officer were picked up by HMCS Timmins (K 223) (T/A/LtCdr J.M. Gillison, RCNR), which then stood by the abandoned Empire Sailor all night. At dawn, a boarding party of four men equipped with gas masks reboarded the vessel to search for the three missing crewmen and to see if the ship could be salvaged. These were the chief officer, the second officer, a mess room steward and a naval signalman. They discovered that the ship had righted herself, but settled by the stern because the engine room, #4 and #5 holds were flooded. Nobody was found aboard except a Dachshund who had been part of the cargo and had the good sense to seek refuge on the top bridge in clean air while the ship’s cat was found dead. The dog was taken aboard the corvette when the boarding party returned after about half an hour due to the presence of the poison gas. HMCS Timmins requested assistance by tugs, however at 14.20 hours the ship suddenly reared up by the bows and sank by the stern, possibly after the bulkhead between #5 and #6 hold has given way. The three depth charges on the stern exploded soon after she sank.

The ordeal of the survivors had only just begun as the time the phosgene gas took effect varied from 2 to 26 hours, the men did not appear to suffer but would start coughing, froth at the mouth, choke and die in agony. After returning to convoy, the commander of HMCS Minas asked for medical advice how to treat the poisoned survivors and at dawn the medical officer of HMS Wanderer (D 74) (LtCdr D.H.P. Gardiner, DSC, RN) was transferred to the minesweeper to assist. He later returned to the destroyer with eight survivors who were landed at Halifax on 23 November. Fourteen survivors died at sea before HMCS Minas reached Halifax in the evening of 22 November. One more died whilst on the way to the hospital. Four of the 17 survivors picked up by HMCS Timmins also died before the corvette reached Halifax a few hours earlier than HMCS Minas and a fifth died in a hospital. In all, three crewmen were lost in the attack and 17 crew members and three gunners died from phosgene gas poisoning.

Extract from a report to the Admiralty by the commander of HMS Wanderer:
No precautions had been taken onboard, apparently only the senior officers being aware of the nature of the cargo. If the crew had carried ordinary service respirators they would have been adequately protected. These respirators were not even carried on board. It is submitted that these facts should be made the subject for a full enquiry, as it seems that there are some who do not realize that our Merchant Navy have enough to put up with without having to die horrible deaths caused by their own cargo. The effect of this occurrence on the morale of Merchant Seamen in Halifax can readily be imagined.