Air Force Two is the air traffic control designated call sign held by any United States Air Force aircraft carrying the vice president of the United States, but not the president. The term is often associated with the Boeing C-32, a modified 757 which is most commonly used as the vice president's transport. Other 89th Airlift Wing aircraft, such as the Boeing C-40 Clipper, C-20B, C-37A, and C-37B, have also served in this role. The VC-25A, the aircraft most often used by the president as Air Force One, has also been used by the vice president as Air Force Two.