High Quality Content by WIKIPEDIA articles! KC-X is the United States Air Force (USAF) program to procure its next-generation aerial refueling tanker aircraft to replace some of the older Boeing KC-135 Stratotankers. The contest was for a production contract for 179 new tankers with estimated value of US$35 billion. The two contenders to replace the KC-135 aircraft were Boeing and EADS, following the elimination of US Aerospace, Inc.