|I learned recently that the world's largest air force is the United States Air Force, with 5484 aircraft. The world's second largest air force is the United States Navy, with 3700 aircraft. The next largest force is Russia's, with about 1900 aircraft.
On a related note, I once heard someone say the Navy has its own air force and its own army (the Marine Corps). And in reference to the Marines' purchase of aircraft, an Army officer was quoted as saying, "Why does the Navy's army need its own air force?"