The Battle of the Atlantic pitted U-boats and other warships of the German "Kriegsmarine" (Navy) and aircraft of the "Luftwaffe" (Air Force) against the Royal Navy, Royal Canadian Navy, United States Navy, and Allied merchant shipping. 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 beginning September 13, 1941. The Germans were joined by submarines of the Italian "Regia Marina" (Royal Navy) after Germany's Axis ally Italy entered the war on June 10, 1940.