The U.S. Air Force Air Mobility Command has suggested their KC-135 Stratotanker fleet may serve beyond 2050 with a life extension and upgrade program.
Almost 70 years after the type’s first flight, the KC-135 Stratotanker remains the U.S. Air Force’s primary and most numerous aerial refueling aircraft. Now supplemented by the KC-46A Pegasus, which will replace some of the oldest KC-135s, the 179 strong Pegasus order is a long way short of the approximately 376 KC-135s still in service. In addition, the shortfall left by the total retirement of the KC-10A Extender also has to be taken into account.
Currently, the Stratotanker fleet’s stated retirement date is 2050, by which time many of the aircraft in service today would be well past their 90th year. The youngest airframe, 64-14840, would be 85 years old.
Studies are currently ongoing to assess the need for new tankers both in the short term and in the long term, with the latter, the Next Generation Air Refueling System (NGAS), investigating the possibility of a stealthy tanker design. If NGAS were to proceed, it would still be many years before the first of the type enters operational service, and even longer before a significant number could be delivered.
According to an Air Mobility Command (AMC) spokesperson, these studies “will determine if there’s a need to extend the service life of the KC-135 beyond its currently planned 2050 sunset. If extended, the fleet will likely undergo major modifications and enhancements”.
Since entering service, the KC-135 fleet has already received a significant amount of upgrades and refurbishment programs. Three variants of the KC-135 are currently in operational service with the U.S. Air Force: the KC-135R makes up the bulk of the fleet, while the former SR-71 Blackbird-specialized KC-135Q tankers are now designated KC-135T and still have the ability to isolate some of their tanks from the jet’s own fuel supply.
Updated with new CFM engines, and modern avionics, the KC-135 is wonderfully analogue. Pulleys & cables for controls, a veritable wall of circuit breakers, & air conditioning that has two settings ‘freezer’ & ‘sauna’. Love it! #avgeek pic.twitter.com/hZilOm1HgA
— Tim Robinson (@RAeSTimR) June 6, 2023
Finally, the KC-135RT is a rare special operations-focused variant that adds the capability for the aircraft itself to be refueled in the air. These aircraft are operated by the 22nd Operations Group Special Operations Air Refueling (SOAR) division (not to be confused with the U.S. Army 160th Special Operations Aviation Regiment). Along with the unit’s other tankers, the KC-135RTs are also outfitted with additional communications equipment and their crews train extensively for operating at night and under strict radio silence procedures.
Whether or not we will see more KC-135 designations in the future to denote upgraded airframes, like with the B-52H to B-52J modernization, remains to be seen. Importantly, unlike the B-52, the final KC-135s to use the TF33 engine were retired in 2009 with all aircraft currently in USAF service instead using the more modern high bypass turbofan CFM56 (F108 in USAF service) engine. This same engine is widely used in the civilian world on Boeing 737s and Airbus A320 airliners, meaning there is a more than sufficient supply of spares and technical knowledge available.
Retirement of portions of the overall Stratotanker force as more KC-46s are delivered will add to the already large supply of spares, though significant issues with the new tanker may force some aircraft to soldier on for longer than expected. Deliveries of the KC-46 are presently halted due to cracks discovered on aircraft being prepared for delivery.
The bridge tanker program, which is intended to ensure tanker availability in the short to medium term with a planned buy of 75 airframes, is yet to have an aircraft selected. The KC-46 would, in theory, be the obvious choice, but the ongoing issues are sure to have dissuaded Air Force planners.
The KC-46’s primary competitor in the global market is Airbus’ A330 MRTT, which was originally chosen by the U.S. Air Force as the KC-45 before a successful protest was lodged by Boeing. It looks unlikely that Airbus and partner Lockheed Martin will offer the aircraft for this contract, leaving the Air Force very short of alternatives. An L3Harris proposal to develop a tanker variant of the C-390 Millennium with Embraer for the USAF has also been canceled.
Special Missions
The KC-135 is one of several aircraft types in the USAF inventory that use the C-135 Stratolifter airframe. Notably, though it shares a common ancestor with the Boeing 707 on which the E-3 Sentry and E-6 Mercury are based, the C-135 is in fact a different airframe altogether.
The most numerous and most famous non-tanker C-135 variant still in USAF service is the RC-135. RC-135V/W Rivet Joints are the USAF’s primary manned signals intelligence (SIGINT) platform and make up most of the RC-135 force. There is also the RC-135S Cobra Ball, which is dedicated to gathering measurement and signature intelligence (MASINT) on ballistic missile launches, as well as the RC-135U Combat Sent which is specialized for intercepting and analyzing radar emissions. The RC-135 force is supported by a small collection of TC-135Ws which outwardly appear like RC-135s but are instead used for crew training.
Three WC-135R Constant Phoenix ‘nuke sniffer’ aircraft are used to take atmospheric samples and monitor for radioactive isotopes that could be released by secret nuclear weapons testing. WC-135s can also be used to monitor releases of radiation from nuclear power plants, and were deployed to gather samples during both the Chernobyl and Fukushima nuclear disasters.
US Air Force conducts an Aircraft Radiological Recovery Plan training event with a WC-135 Constant Phoenix at Royal Air Force Mildenhall, UK, May. 11. pic.twitter.com/ZVeivoIW71
— Ryan Chan 陳家翹 (@ryankakiuchan) May 15, 2023
No immediate plans exist for the replacement of any of these special mission C-135 variants, and in fact the two WC-135R aircraft have only recently entered service to replace ageing WC-135Cs. They were converted from KC-135R airframes.
With the complex nature of procurement, and the even more complex nature of constructing an airframe for intelligence missions, it is certainly possible that these distinctive white and grey aircraft might join their tanker cousins in celebrating their 100th anniversaries in the decades to come.
