What was the Battle of the Atlantic?

The Battle of the Atlantic was the longest continuous military campaign of the Second World War, lasting from September 1939 to May 1945 (the war's full duration in Europe). Allied warships and aircraft including the Royal Canadian Navy (RCN) protected merchant convoys carrying supplies from North America to Britain against German U-boats, surface ships, and aircraft. The Royal Canadian Navy played a central role, growing from about 1,800 personnel in 1939 to about 100,000 by 1945 and becoming the third-largest Allied navy after the United States Navy and the British Royal Navy.

Halifax was the principal Canadian convoy port. Eastbound convoys (carrying war materiel, food, fuel, troops, and equipment from North America to Britain) and westbound convoys (returning) departed regularly throughout the war. The Slow Convoy (SC) and Halifax Outbound (HX) convoys were two of the principal series. About 25,000 convoy crossings of the North Atlantic took place during the war, totalling about 165 million tons of supplies. The RCN escorted about half of all Allied convoys in the western Atlantic from 1942 onward.

The campaign passed through several phases. The early period (1939 to 1941) saw German surface raiders (the Bismarck, Tirpitz, and pocket battleships Graf Spee, Scheer, and Lützow) and early U-boat operations. The crisis period (1942 to mid-1943) saw the height of U-boat warfare, with Admiral Karl Dönitz's wolf-pack tactics sinking enormous tonnage. May 1943 was the decisive month; the Allies sank 41 U-boats while losing only 50 merchant ships, leading Dönitz to withdraw most U-boats from the North Atlantic convoy routes (the 'Black May' for the U-boat force). The late period (1943 to 1945) saw diminished German operations but continuing convoy duty.

Canadian losses were significant. About 4,600 RCN sailors died, plus about 1,800 Royal Canadian Air Force personnel and about 2,200 Canadian merchant seamen. The RCN lost 24 warships, including the destroyers Athabaskan, Margaree, and Saguenay; the corvettes Levis, Spikenard, and many others; and the minesweeper Mulgrave. Notable Canadian Battle of the Atlantic actions included the sinking of the Italian submarine Tritone by HMCS Port Arthur (January 19, 1943) and the depth-charging of U-94 by HMCS Oakville (August 28, 1942). The Canadian Naval Memorial Trust preserves HMCS Sackville, a Flower-class corvette, in Halifax as a museum ship and memorial to the Battle of the Atlantic. Battle of the Atlantic Sunday is commemorated on the first Sunday of May.