The Royal Air Force is the aerial warfare force of the United Kingdom, founded on 1 April 1918 at the end of World War I to replace the Royal Flying Corps. The RAF emerged as one of the strongest air forces of the time, defeating Nazi Germany's Luftwaffe in the 1940-1941 Battle of Britain and taking part in the bombing of Germany during the war. The RAF remains one of the most important air forces in the world alongside its ally, the US Air Force, with 34,200 troops and 793 aircraft in 2015, at the time of its engagement in Operation Inherent Resolve.