Happy 73rd Birthday to the United States Air Force! The U.S. Air Force is the world’s preeminent force in air, space and cyberspace. From its humble beginnings as the Signal Corps in 1907, the U.S. Air Force has become the largest air power in the world. The official Air Force Birthday is recognized as September 18, 1947, the date of the passage of the National Security Act, which created the Department of the Air Force. For over a century now, the U.S. Air Force has defended this country in the air, space and cyberspace through the skill and the bravery of American Airmen.