The United States Air Force (USAF) is the aerial warfare service branch of the United States Armed Forces. The USAF Unit is a term used to refer to the various units that make up the USAF. The two most common USAF Units are the Strategic Air Command (SAC) and the Combatant Command (CMD). SAC is responsible for the organization, training, and equipping of air forces for global operations while CMD is responsible for planning, organizing, and executing military operations.