The 59 KC-10 Extender tankers, originally acquired in the 1980s by SAC, have been operated largely in the refueling of large number of fighter aircraft on ferry flights, the refueling of other transport aircraft, or as supplemental airlift aircraft for palletized cargo, augmenting the C-5 and C-17 fleet. Conversely, the KC-135 fleet has operated largely in the in-theater role. In an attempt to modernize the platform, the USAF has awarded Boeing a US$216 million contract to upgrade its fleet of 59 aircraft with new Communication, navigation and surveillance and air traffic management system to operate into the 2020s.