The power of Congress to create an air force is not written in the Constitution. However, Congress had the authority to create one, as part of its expressed powers to support armies. Which provision in the Constitution allowed Congress to establish an air force?

Article 1 section 8 of the constitution states that the congress has the power to support and raise armies as well as to provide and maintain a navy. Since having an airforce is a part of the idea of raising an army, and because the navy also has aircraft among its vehicles and trained pilots as troops, their establishment of an airforce is not unconstitutional.