page_title: Boeing KC-135 Stratotanker
section_title: Replacing the KC-135
hierarchical_section_title: Boeing KC-135 Stratotanker / Operational history / Replacing the KC-135
caption_attribution_description: English: The view from the boom operator's hatch as a F-35 fuels from a KC-135 of the 912d ARS
context_page_description: The Boeing KC-135 Stratotanker is a military aerial refueling aircraft that was developed from the Boeing 367-80 prototype, alongside the Boeing 707 airliner. It is the predominant variant of the C-135 Stratolifter family of transport aircraft. The KC-135 was the US Air Force's first jet-powered refueling tanker and replaced the KC-97 Stratofreighter. The KC-135 was initially tasked with refueling strategic bombers, but it was used extensively in the Vietnam War and later conflicts such as Operation Desert Storm to extend the range and endurance of US tactical fighters and bombers.
  The KC-135 entered service with the United States Air Force in 1957; it is one of six military fixed-wing aircraft with over 50 years of continuous service with its original operator. The KC-135 is supplemented by the larger KC-10. Studies have concluded that many of the aircraft could be flown until 2030, although maintenance costs have greatly increased. The KC-135 is to be partially replaced by the Boeing KC-46 Pegasus.
context_section_description: Between 1993 and 2003, the amount of KC-135 depot maintenance work doubled, and the overhaul cost per aircraft tripled. In 1996, it cost $8,400 per flight hour for the KC-135, and in 2002 this had grown to $11,000.  The Air Force's 15-year estimates project further significant cost growth through fiscal year 2017. KC-135 fleet operations and support costs are estimated to grow from about $2.2 billion in fiscal year 2003 to $5.1 billion (2003 dollars) in fiscal year 2017, an increase of over 130 percent, which represents an annual growth rate of about 6.2 percent.
  The Air Force projected that E and R models have lifetime flying hour limits of 36,000 and 39,000 hours, respectively.  According to the Air Force, only a few KC-135s would reach these limits by 2040, when some aircraft would be about 80 years old. A later 2005 Air Force study estimated that KC-135Es upgraded to the R standard could remain in use until 2030.
  In 2006, the KC-135E fleet was flying an annual average of 350 hours per aircraft and the KC-135R fleet was flying an annual average of 710 hours per aircraft.  The KC-135 fleet is currently flying double its planned yearly flying hour program to meet airborne refueling requirements, and has resulted in higher than forecast usage and sustainment costs. In March 2009, the Air Force indicated that KC-135s would require additional skin replacement to allow their continued use beyond 2018.
  The USAF decided to replace the KC-135 fleet.  However, the KC-135 fleet is large and will need to be replaced gradually.  Initially the first batch of replacement planes was to be an air tanker version of the Boeing 767, leased from Boeing.  In 2003, this was changed to contract where the Air Force would purchase 80 KC-767 aircraft and lease 20 more. In December 2003, the Pentagon froze the contract and in January 2006, the KC-767 contract was canceled.  This followed public revelations of corruption in how the contract was awarded, as well as controversy regarding the original leasing rather than outright purchase agreement.  Then Secretary of Defense Rumsfeld stated that this move will in no way impair the Air Force's ability to deliver the mission of the KC-767, which will be accomplished by continuing upgrades to the KC-135 and KC-10 Extender fleet.
  In January 2007, the U.S. Air Force formally launched the KC-X program with a request for proposal (RFP).  KC-X is first phase of three acquisition programs to replace the KC-135 fleet. On 29 February 2008, the US Defense Department announced that it had selected the EADS/Northrop Grumman "KC-30" (to be designated the KC-45A) over the Boeing KC-767. Boeing protested the award on 11 March 2008, citing irregularities in the competition and bid evaluation. On 18 June 2008, the US Government Accountability Office sustained Boeing's protest of the selection of the Northrop Grumman/EADS's tanker. In February 2010, the US Air Force restarted the KC-X competition with the release of a revised request for proposal (RFP). After evaluating bids, the USAF selected Boeing's 767-based tanker design, with the military designation KC-46, as a replacement in February 2011. The first KC-46A Pegasus was delivered to the U.S. Air Force on 10 January 2019.
  In April 2020, plans call for retiring KC-135s, which are supposed to be replaced by KC-46s. But the KC-46 has been challenged by development delays that leave them non-operational.  These would leave a gap in the USAF's future ability to fulfill operational refueling.
  Two foreign users of the KC-135, the French Air Force and the Republic of Singapore Air Force are taking deliveries of Airbus A330 MRTTs as replacements for their Stratotankers.
caption: View from the boom operator's hatch as a F-35 takes on fuel from a KC-135 of the 912d ARS
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