Boeing KC - 135 Stratotanker The Boeing KC - 135 Stratotanker is a military aerial refueling aircraft . It and the Boeing 707 airliner were developed from the Boeing 367 - 80 prototype . The KC - 135 was the US Air Force ' s first jet - powered refueling tanker and replaced the KC - 97 Stratotanker . The Stratotanker was initially tasked to refuel strategic bombers , but 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 ( USAF ) 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 . Despite increased maintenance costs , studies conclude many of the aircraft could be flown until 2040 . The aircraft will eventually be replaced by the Boeing KC - 46 . Development . Background . Like its sibling , the commercial Boeing 707 jet airliner , the KC - 135 was derived from the Boeing 367 - 80 jet transport " proof of concept " demonstrator , which was commonly called the " Dash - 80 " . As such the KC - 135 is similar in appearance to the 707 , but has a narrower fuselage and is shorter than the 707 . The KC - 135 predates the 707 , and is structurally quite different from the civilian airliner . Boeing gave the future KC - 135 tanker the initial designation Model 717 . In 1954 USAF ' s Strategic Air Command held a competition for a jet - powered aerial refueling tanker . Lockheed ' s tanker version of the proposed Lockheed L - 193 airliner with tail - mounted engines was declared the winner in 1955 . Since Boeing ' s proposal was already flying , the KC - 135 could be delivered two years earlier and Air Force Secretary Harold E . Talbott ordered 250 KC - 135 tankers until the Lockheed ' s design could be manufactured . In the end , orders for the Lockheed tanker were dropped rather than supporting two tanker designs . Lockheed never produced its jet airliner , while Boeing would eventually dominate the market with a family of airliners based on the 707 . In 1954 the Air Force placed an initial order for 29 KC - 135As , the first of an eventual 820 of all variants of the basic C - 135 family . The first aircraft flew in August 1956 and the initial production Stratotanker was delivered to Castle Air Force Base , California , in June 1957 . The last KC - 135 was delivered to the Air Force in 1965 . Developed in the early 1950s , the basic airframe is characterized by 35 - degree aft swept wings and tail , four underwing - mounted engine pods , a horizontal stabilizer mounted on the fuselage near the bottom of the vertical stabilizer with positive dihedral on the two horizontal planes and a hi - frequency radio antenna which protrudes forward from the top of the vertical fin or stabilizer . These basic features make it strongly resemble the commercial Boeing 707 and 720 aircraft , although it is actually a different aircraft . Reconnaissance and command post variants of the aircraft , including the RC - 135 Rivet Joint and EC - 135 Looking Glass Post Attack Command & Control Systems were operated by SAC from 1963 through 1992 , when they were re - assigned to the Air Combat Command ( ACC ) . The USAF EC - 135 Looking Glass was subsequently replaced in its role by the U . S . Navy E - 6 Mercury aircraft , a new build airframe based on the Boeing 707 - 320B . General upgrades . The KC - 135Q variant was modified to carry JP - 7 fuel necessary for the SR - 71 Blackbird , segregating the JP - 7 from the KC - 135 ' s own fuel supply ( the body tanks carrying JP - 7 , and the wing tanks carrying JP - 4 or JP - 8 ) . When the KC - 135Q model received the CFM - 56 engines , it was redesignated the KC - 135T model , which was capable of separating the main body tanks from the wing tanks where the KC - 135 draws its engine fuel . The only external difference between a KC - 135R and a KC - 135T is the presence of a clear window on the underside of the empennage of the KC - 135T where a remote controlled searchlight is mounted . It also has two ground refueling ports , located in each rear wheel well so ground crews can fuel both the body tanks and wing tanks separately . Eight KC - 135R aircraft are receiver - capable tankers , commonly referred to as KC - 135R ( RT ) . All eight aircraft were with the 22d Air Refueling Wing at McConnell AFB , KS as of 1994 . They are primarily used for force extension and Special Operations missions , and are crewed by highly qualified receiver capable crews . If not used for the receiver mission , these aircraft can be flown just like any other KC - 135R . In order to expand the KC - 135 ' s capabilities and improve its reliability , the aircraft has undergone a number of upgrades . Among these was the Pacer - CRAG program ( CRAG = " Compass , Radar And GPS " ) which ran from 1999 to 2002 and modified all the aircraft in the inventory to eliminate the Navigator position from the flight crew . The program development was done by Rockwell Collins in Iowa and installation was performed by BAE Systems at the Mojave Airport in California . The latest block upgrade to the KC - 135 is Block 40 . 5 which allows the KC - 135 to comply with Global air - traffic management . The KC - 135 Block 45 program is expected to come online in 2014 and addresses non - procurable instrument upgrades as well as a new autopilot system . Re - engining . All KC - 135s were originally equipped with Pratt & Whitney J - 57 - P - 59W turbojet engines which produced of thrust dry , and approximately of thrust wet . Wet thrust is achieved through the use of water injection on takeoff . of water are injected into the engines over the course of two and a half minutes . This water allows a second set of fuel injectors to activate without melting the turbine buckets . The water turns to steam and is ejected out the rear of the engine , increasing the exhaust mass and increasing thrust . The engine runs somewhat hotter , with more engine noise . In the 1980s the first modification program re - engined 157 Air Force Reserve ( AFRES ) and Air National Guard ( ANG ) tankers with the Pratt & Whitney TF - 33 - PW - 102 engines from 707 airliners retired in the late 1970s and early 1980s . The re - engined tanker , designated the KC - 135E , was 14 % more fuel efficient than the KC - 135A and could offload 20 % more fuel on long duration flights . ( The difference is that the A - model weighed only empty , while the E - model weighed empty . But the maximum takeoff weight was not increased for the E - model . Therefore , the A - model could takeoff with of fuel , while the E - model could only takeoff with of fuel . ) Only the KC - 135E aircraft were equipped with thrust - reversers for takeoff aborts and shorter landing roll - outs . The KC - 135E fleet has since either been re - engined into the R - model configuration or placed into long term storage ( " XJ " ) , as Congress has prevented the Air Force from formally retiring them . The final KC - 135E , tail number " 56 - 3630 " , was delivered by the 101st Air Refueling Wing of the Maine Air National Guard to the 309th Aerospace Maintenance and Regeneration Group ( AMARG ) at Davis - Monthan Air Force Base in September 2009 . The second modification program re - engined 500 aircraft with new CFM International CFM56 ( military designation : F108 ) engines produced by General Electric and Snecma . The CFM - 56 turbofans are capable of producing approximately of thrust , nearly a 100 % increase in thrust compared to the original J - 57 engines . The re - engined tanker , designated either the KC - 135R ( modified KC - 135A or E ) or KC - 135T ( modified KC - 135Q ) , can offload up to 50 % more fuel ( on a long duration sortie ) , is 25 % more fuel efficient , costs 25 % less to operate and is 96 % quieter than the KC - 135A ( sideline noise levels at takeoff were reduced from 126 to 99 decibels ) . The KC - 135R ' s operational range is 60 % greater than the KC - 135E for comparable fuel offloads , providing a wider range of basing options . No longer in consideration , upgrading the remaining KC - 135E into KC - 135R would have cost about US $ 3 billion , about $ 24 million per aircraft . According to Air Force data , the KC - 135 fleet had a total operation and support cost in fiscal year 2001 of about $ 2 . 2 billion . The older E model aircraft averaged total costs of about $ 4 . 6 million per aircraft , while the R models averaged about $ 3 . 7 million per aircraft . Those costs include personnel , fuel , maintenance , modifications , and spare parts . Further upgrades and derivatives . This program adds refueling pods to the KC - 135 ' s wings . The pods allow refueling of U . S . Navy , U . S . Marine Corps and most NATO tactical jet aircraft while keeping the tail - mounted refueling boom . The pods themselves are Flight Refueling Limited ( FRL ) MK . 32B model pods . This allows the tanker to refuel two receivers at the same time , which increases throughput compared to the boom drogue adapter . A number of KC - 135A and KC - 135B aircraft have been modified to EC - 135 , RC - 135 and OC - 135 configurations for use in several different roles . Design . The KC - 135R has four turbofan engines , mounted under 35 - degree swept wings , which power it to takeoffs at gross weights up to . Nearly all internal fuel can be pumped through the tanker ' s flying boom , the KC - 135 ' s primary fuel transfer method . A special shuttlecock - shaped drogue , attached to and trailing behind the flying boom , may be used to refuel aircraft fitted with probes . A boom operator stationed in the rear of the aircraft controls the boom while lying prone . A cargo deck above the refueling system can hold a mixed load of passengers and cargo . Depending on fuel storage configuration , the KC - 135 can carry up to of cargo . Operational history . Introduction into service . The KC - 135 was initially purchased to support bombers of the Strategic Air Command , but by the late 1960s , in the Southeast Asia theater , the KC - 135 Stratotanker ' s ability as a force multiplier came to the fore . Midair refueling of F - 105 and F - 4 fighter - bombers as well as B - 52 bombers brought far - flung bombing targets within reach , and allowed fighter missions to spend hours at the front , rather than just a few minutes , due to their limited fuel reserves . KC - 135 crews refueled both Air Force and Navy / Marine Corps aircraft , though they would have to change to probe and drogue adapters depending upon the mission . Crews also helped to bring in damaged aircraft which could fly while being fed by fuel to a landing site . KC - 135s continued their tactical support role in later conflicts such as Desert Storm and current aerial strategy . The Strategic Air Command ( SAC ) had the KC - 135 Stratotanker in service with Regular Air Force SAC units from 1957 through 1992 and with SAC - gained Air National Guard ( ANG ) and Air Force Reserve ( AFRES ) units from 1975 through 1992 . Following a major USAF reorganization that resulted in the inactivation of SAC in 1992 , most KC - 135s were re - assigned to the newly created Air Mobility Command ( AMC ) . While AMC gained the preponderance of the aerial refueling mission , a small number of KC - 135s were also assigned directly to United States Air Forces in Europe ( USAFE ) , Pacific Air Forces ( PACAF ) and the Air Education and Training Command ( AETC ) . All Air Force Reserve Command ( AFRC ) KC - 135s and most of the Air National Guard ( ANG ) KC - 135 fleet became operationally - gained by AMC , while Alaska Air National Guard and Hawaii Air National Guard KC - 135s became operationally - gained by PACAF . Air Mobility Command ( AMC ) manages more than 481 Stratotankers , of which the Air Force Reserve Command ( AFRC ) and Air National Guard ( ANG ) fly 292 in support of AMC ' s mission as on April 2008 . The KC - 135 is joined by the Tupolev Tu - 95 , the C - 130 Hercules , the B - 52 Stratofortress , the English Electric Canberra , the Northrop T - 38 Talon and the Lockheed U - 2 in having over 50 years of continuous service with its original operator . Research usage . Besides its primary role as an inflight aircraft refueler , the KC - 135 , designated NKC - 135 , has assisted in several research projects at the NASA Dryden Flight Research Center at Edwards Air Force Base , California . One such project occurred between 1979 and 1980 when special wingtip " winglets " , developed by Richard Whitcomb of the Langley Research Center , were tested at Dryden , using an NKC - 135A tanker loaned to NASA by the Air Force . Winglets are small , nearly vertical fins installed on an aircraft ' s wing tips . The results of the research showed that drag was reduced and range could be increased by as much as 7 percent at cruise speeds . Winglets are now being incorporated into most new commercial and military transport jets , as well as business aviation jets . NASA also has operated several KC - 135 aircraft ( without the tanker equipment installed ) as their infamous Vomit Comet zero - gravity simulator aircraft . The longest - serving ( 1973 to 1995 ) version was KC - 135A , AF Ser . No . " 59 - 1481 " , named " Weightless Wonder IV " and registered as N930NA . Replacing the KC - 135 . As of 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 . The Air Force projects 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 before 2040 , but at that time some of the aircraft would be about 80 years old . The Air Force estimates that their current fleet of KC - 135s have between 12 , 000 to 14 , 000 flying hours on them - only 33 percent of the lifetime flying hour limit . Nevertheless these aircraft are over 40 years old and maintenance costs are increasing , with airframe corrosion being the worst problem . 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 cost estimates project further significant growth through fiscal year 2017 . For example , operations and support costs for the KC - 135 fleet 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 $ 2 . 9 billion , or over 130 percent , which represents an annual growth rate of about 6 . 2 percent . 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 . On 18 June 2008 , the US Government Accountability Office sustained Boeing ' s protest of the selection of the Northrop Grumman / EADS ' s tanker . In 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 the Boeing 767 design , with the military designation KC - 46 , as a replacement in February 2011 . Variants . " See Boeing C - 135 Stratolifter for further details on the C - 135 family . " Note Italy has been reported in some sources as operating several KC - 135s , however these are actually Boeing 707 - 300s converted to tanker configuration . Operators . Israel was offered KC - 135s again in 2013 , after turning down the ancient aircraft twice due to expense of keeping them flying . The IAF again rejected the offered KC - 135Es , but said that it would consider as many as a dozen of the newer KC - 135Rs .