to the United States for help. In response, Franklin D. Roosevelt issued an executive order authorizing the transfer of 50 over-aged destroyers to the British in return for 99-year leases on strategic base sites in the Western Hemisphere. Thatcher was accordingly withdrawn from the Atlantic Squadron and her operations with Destroyer Division 69 for transfer to the Royal Canadian Navy, which had been allocated six of the "50 ships that saved the world," as these vessels came to be known. As such, Thatcher and her five sisters arrived at Halifax, Nova Scotia, on 20 September—the third group of the "flush deckers" transferred. Decommissioned on 24 September 1940, Thatcher was struck from the Navy list on 8 January 1941. Royal Canadian Navy Renamed HMCS Niagara following the Canadian practice of naming destroyers after Canadian rivers (but with deference to the U.S. origin), after the Niagara River forming the border between New York and Ontario. Niagara departed Halifax on 30 November; proceeded eastward via St. John's, Newfoundland; and arrived in the British Isles on 11 December. Early in 1941, the destroyer was allocated to the 4th Escort Group, Western Approaches Command, and based at Greenock, Scotland. Subsequently transferred to the Newfoundland escort force, Niagara operated on convoy escort duties into the summer of 1941. While she was operating with this force, she took part in the capture of a German U-boat, U-570. A Lockheed Hudson bomber, flying from Kaldaðarnes, southeast of Reykjavík, Iceland, located U-570 running on the surface off the Icelandic coast on 27 August 1941. The Hudson attacked the U-boat with depth charges, damaging the enemy craft so severely that she could not submerge. Soon, some of the German crew appeared on deck displaying a large white cloth — possibly a bed sheet — indicating that they had surrendered. Patently unable to capture the submarine herself, the Hudson radioed for help. Niagara sped to the scene and arrived at 08:20 on 28 August 1941. Rough weather initially hampered the operation but eventually, by 18:00, Niagara had placed a prize crew aboard the submarine and had taken U-570 in tow. During the operation, she also took the 43-man crew of the enemy craft on board. Towed to Þorlákshöfn, Iceland, the U-boat eventually served in the Royal Navy as . In January 1942, Niagara escorted the tempest-battered Danish merchantman Triton into Belfast, Northern Ireland, after the freighter had been severely mauled in