The KC-10 Extender first flew on 12 July 1980; October 1980 the first aerial refuel sortie was performed. The design for the KC-10 involved modifications from the DC-10-30CF design. Unnecessary airline features were replaced by an improved cargo-handling system and military avionics. The KC-10 retains 88% commonality with its commercial counterparts, giving it greater access to the worldwide commercial support system. Other changes from the DC-10-30CF include the removal of most windows and lower cargo doors.