The Battle of the Atlantic was the longest continuous battle of the Second World War.
Just hours after Britain formally declared war on Germany on September 3, 1939, the battle for the Atlantic began. A German U-30 submarine torpedoed the SS Athenia just off the coast of Ireland. The passenger ship was en route to Montreal. Of the 1,400 passengers and crew on board, 112 were killed, 4 of which were Canadian.
Canada declared war on Germany a week later on September 10, 1939.