The C-21 Learjet is the military version of the a twin-engine Gates (a subsidiary of Bombardier in Canada) 35A business jet. It provides cargo and passenger airlift and can transport litters during medical evacuations. Eighty-four C-21As were acquired by the USAF in 1984 to be used as an Operational Support Aircraft.
Delivery of the C-21A fleet began in April 1984 and was completed in October 1985. On 1 April 1997, all continental U.S.-based C-21s were realigned under the Air Mobility Command, with the 375th Airlift Wing at Scott Air Force Base, Ill. as the home base. C-21s stationed outside the continental United States are assigned to the theater commanders.