With the entry of the United States into the war on 7 December 1941, Admiral Karl Dönitz, commander of the German U-boat (submarine) fleet, extended operations to the American east coast and the Gulf of St. Lawrence. Initially, the U.S. navy did not employ the convoy system. American merchant ships bound for Halifax sailed individually without any escorts. However, German U-boats sank several American merchant vessels along the East Coast. As a result, the Americans adopted the convoy system, and corvettes of the Royal Canadian Navy (RCN) assumed some of the escort duties for U.S. convoys from New York and Boston to Halifax.
In the first week of May 1942, the German submarine U-553 entered the Gulf of St. Lawrence. On 10 May, a Royal Canadian Air Force Catalina aircraft sighted the U-553 off the Gaspé coast and dropped bombs. The German U-boat submerged and sustained no damage. Two days later, the U-553 torpedoed the British freighter Nicoya and, a few hours later, attacked and sunk another merchant ship.
Until U-553 had attacked shipping in the Gulf of St. Lawrence, merchant vessels had sailed from Quebec to Sydney alone. On 21 May 1942, escorted convoys were established on the Quebec-Sydney route. On 1 June, the RCN organized the Gulf Escort Force, which initially consisted of five Bangor minesweepers and three Fairmile MLs (motor launches: small wooden patrol craft). The motor launches were 30 metres in length and armed with 20 depth charges, a 3-pounder deck gun, and machine guns. By September, the force had, with the addition of 7 corvettes and 3 more MLs, expanded to a force of 19 vessels.