With the stroke of a pen, President Harry S. Truman signed the National Security Act of 1947 on Sept. 18, 1947.

The Act created the National Military Establishment – later renamed the Department of Defense – and created the U.S. Air Force as a separate branch of the U.S. military.

The signing began a three-year transition period in which soldiers became airmen and army air fields became air force bases.

Before that, the responsibility for military aviation was divided between the U.S. Army for land-based operations and the U.S. Navy for sea-based operations.

And while we celebrate the 70th anniversary of the creation of the U.S. Air Force on Sept. 18, the history of U.S. military aviation can be traced back to 1907, when the U.S. Army created the Aeronautical Division, Signal Corps.