An air force in the broadest sense is the national military branch that primarily conducts aerial warfare. More specifically, it is the branch of a nation's armed services that is responsible for aerial warfare as distinct from an army aviation or naval aviation units. Typically, air forces are responsible for gaining control of the air, carrying out strategic and tactical bombing missions, and providing support to land and naval forces often in the form of aerial reconnaissance and close air support.

An army aviation unit is an aviation-related unit of a nation's army, sometimes described as an air corps. These units are generally separate from a nation's dedicated air force, and usually comprise helicopters and light support fixed-wing aircraft. Prior to the establishment of separate national air forces, many armies had military aviation units, which as the importance of aviation increased, were spun off into independent services. As the separation between a nation's army and air force led to a divergence of priorities, many armies sought to re-establish their own aviation branches to best serve their own organic tactical needs.