The Battle of the Atlantic pitted U-boats and other warships of the Kriegsmarine (German navy) and aircraft of the Luftwaffe (German Air Force) against the Royal Canadian Navy, Royal Navy, the United States Navy, and Allied merchant shipping. The convoys, coming mainly from North America and predominantly going to the United Kingdom and the Soviet Union, were protected for the most part by the British and Canadian navies and air forces. These forces were aided by ships and aircraft of the United States from September 13, 1941.The Germans were joined by submarines of the Italian Royal Navy (Regia Marina) after their Axis ally Italy entered the war on June 10, 1940.