History of Boeing KC-135 Stratotanker in Timeline
The Boeing KC-135 Stratotanker is a crucial American military aerial refueling tanker aircraft. Derived from the Boeing 367-80 prototype (also the basis for the 707 airliner), it features a narrower and shorter fuselage compared to the 707. Boeing internally designated it as Model 717, a designation later used for another aircraft. The KC-135's primary function is to extend the range and endurance of military aircraft by providing in-flight refueling capabilities, making it a vital asset for global air operations.
1 hour ago : KC-135 Damaged, Another 'Missing' Over Qatar, and Sends Emergency Signal
A KC-135 Stratotanker, damaged by shrapnel, is heading to Tinker AFB. Separately, another USAF tanker vanished over Qatar after sending an emergency signal, triggering concerns and searches.
1950: USAF Operated First Aerial Tanker
In 1950, the USAF operated the world's first production aerial tanker, the Boeing KC-97 Stratofreighter. It was a gasoline-fueled, piston-engined Boeing Stratocruiser with a Boeing-developed flying boom and extra kerosene tanks.
1954: Initial Order for KC-135As
In 1954, the USAF placed an initial order for 29 KC-135As, marking the start of production for the C-135 family of aircraft.
1954: USAF Held Competition for Jet-Powered Tanker
In 1954, the USAF's Strategic Air Command (SAC) held a competition for a jet-powered aerial-refueling tanker.
1955: KC-135 Tanker Ordered
In 1955, the Lockheed Corporation tanker version of the proposed Lockheed L-193 airliner was initially declared the winner of the competition. However, Air Force Secretary Harold E. Talbott ordered 250 KC-135 tankers because Boeing's proposal was already flying and could be delivered two years earlier. Eventually, the Lockheed tanker orders were dropped.
1955: Entry into Service
Since entering into service in 1955, 52 Stratotankers have been lost to accidents, involving 385 fatalities.
August 1956: First Flight of KC-135
In August 1956, the first KC-135 aircraft completed its maiden flight.
June 1957: Initial Production Stratotanker Delivered
In June 1957, the initial-production Stratotanker was delivered to Castle Air Force Base, California.
1957: KC-135 in Service with Regular Air Force SAC Units
From 1957 the KC-135 Stratotanker was in service with Regular Air Force SAC units.
1957: KC-135 Entered USAF Service
In 1957, the KC-135 Stratotanker entered service with the United States Air Force. It became one of a few military fixed-wing aircraft to have over 60 years of continuous service with its original operator.
1963: Introduction of Reconnaissance and Command Post Variants
In 1963, reconnaissance and command post variants of the KC-135 aircraft, including the RC-135 Rivet Joint and EC-135 Looking Glass aircraft, were operated by SAC.
1965: Last KC-135 Delivered to USAF
In 1965, the last KC-135 was delivered to the USAF, completing the initial production run.
1967: Crash Replacement
In 1967, JC/KC-135A with serial number 58-0126 replaced aircraft 59-1465 after it crashed.
1973: NASA Operated KC-135 as Vomit Comet
From 1973 to 1995, NASA operated several KC-135 aircraft as their Vomit Comet zero-gravity simulator aircraft. The longest-serving version was KC-135A, AF Ser. No. 59-1481, named Weightless Wonder IV.
1975: KC-135 in Service with SAC-gained ANG and AFR Units
From 1975 the KC-135 Stratotanker was in service with SAC-gained ANG and AFR units.
1979: Winglet Testing Project
Between 1979 and 1980, the KC-135, designated NKC-135, assisted in a research project at the NASA Armstrong Flight Research Center at Edwards Air Force Base, California, to test special wingtip "winglets".
1979: RC-135A Modification
In 1979, all four RC-135A aircraft were modified to a partial KC-135A configuration and designated KC-135D.
1980: Winglet Testing Project
Between 1979 and 1980, the KC-135, designated NKC-135, assisted in a research project at the NASA Armstrong Flight Research Center at Edwards Air Force Base, California, to test special wingtip "winglets".
1984: EC-135Y Modification
In 1984, an airborne command post was modified to support CINCCENT, resulting in aircraft 55-3125 becoming the only EC-135Y.
1985: C-135F Upgrade
In 1985, 11 surviving C-135F aircraft began to be upgraded with CFM International F108 turbofans.
1988: C-135F Upgrade Completion
By 1988, the upgrade of 11 surviving C-135F aircraft with CFM International F108 turbofans was completed. These aircraft were later modified with MPRS wing pods.
1990: Re-engining and Cockpit Update
In 1990, the modified KC-135D aircraft were re-engined with Pratt & Whitney TF33 engines and received a cockpit update to KC-135E standards.
1992: SAC Inactivation and Reassignment of KC-135s
Following a major USAF reorganization in 1992, Strategic Air Command (SAC) was inactivated, and most KC-135s were reassigned to the newly created Air Mobility Command (AMC).
1992: Reassignment of Reconnaissance and Command Post Variants
In 1992, the RC-135 Rivet Joint and EC-135 Looking Glass aircraft were reassigned from SAC to the Air Combat Command following a major USAF reorganization.
1993: Increase in KC-135 Depot Maintenance Work
Between 1993 and 2003, the amount of KC-135 depot maintenance work doubled, and the overhaul cost per aircraft tripled.
1994: KC-135R Aircraft with 22d Air Refueling Wing
In 1994, all eight KC-135R aircraft capable of receiving fuel were with the 22d Air Refueling Wing at McConnell AFB, Kansas. These aircraft were primarily used for force extension and special operations missions.
1995: NASA Operated KC-135 as Vomit Comet
From 1973 to 1995, NASA operated several KC-135 aircraft as their Vomit Comet zero-gravity simulator aircraft. The longest-serving version was KC-135A, AF Ser. No. 59-1481, named Weightless Wonder IV.
1996: Cost Per Flight Hour in 1996
In 1996, the cost per flight hour for the KC-135 was $8,400.
1999: Pacer-CRAG Program Started
In 1999, the Pacer-CRAG program (compass, radar, and GPS) was initiated to upgrade the KC-135's avionics and improve reliability.
2001: KC-135 Fleet Operation and Support Costs in 2001
According to USAF data, in fiscal year 2001, the KC-135 fleet had a total operation and support cost of about $2.2 billion, with older E model aircraft averaging $4.6 million per aircraft and R models averaging about $3.7 million per aircraft.
2002: Pacer-CRAG Program Completed
In 2002, the Pacer-CRAG program was completed, modifying all aircraft in the KC-135 inventory to eliminate the navigator position from the flight crew. The fuel-management system was also replaced.
2002: Cost Per Flight Hour in 2002
In 2002, the cost per flight hour for the KC-135 had grown to $11,000.
December 2003: Pentagon Froze KC-767 Contract
In December 2003, the Pentagon froze the contract for the air tanker version of the Boeing 767, to be leased from Boeing.
2003: Increase in KC-135 Depot Maintenance Work
Between 1993 and 2003, the amount of KC-135 depot maintenance work doubled, and the overhaul cost per aircraft tripled.
2004: Projected Cost Growth to Fiscal Year 2017
In 2004, the USAF's 15-year estimates projected significant cost growth to fiscal year 2017.
2005: USAF Study on KC-135E Upgrades
In 2005, a USAF study estimated that KC-135Es upgraded to the R standard could remain in use until 2030.
January 2006: Cancellation of KC-767 Contract
In January 2006, the contract for the KC-767 was canceled due to public revelations of corruption in how the contract was awarded and controversy regarding the original leasing rather than outright purchase agreement.
2006: Annual Flying Hours for KC-135E and KC-135R Fleets
In 2006, the KC-135E fleet was flying an annual average of 350 hours per aircraft, while the KC-135R fleet was flying an annual average of 710 hours per aircraft.
January 2007: USAF Launched KC-X Program
In January 2007, the USAF launched the KC-X program with a request for proposal (RFP) to replace the KC-135 fleet.
2007: Retirement to AMARG
In 2007, the re-engined and updated KC-135E aircraft were retired to the 309th AMARG at Davis-Monthan AFB, AZ.
February 2008: Selection of EADS/Northrop Grumman KC-30
In February 2008, the US Defense Department selected the EADS/Northrop Grumman "KC-30" (to be designated the KC-45A) over the Boeing KC-767.
March 2008: Boeing Protested Award
In March 2008, Boeing protested the award, citing irregularities in the competition and bid evaluation.
March 2009: Requirement for Skin Replacement
In March 2009, the Air Force indicated that KC-135s would require additional skin replacement to allow their continued use beyond 2018.
September 2009: E Model Aircraft Retirement
By September 2009, all E model aircraft were retired to the 309th AMARG at Davis-Monthan AFB and replaced with R models.
September 2009: Final KC-135E Delivered for Storage
In September 2009, the final KC-135E, tail number 56-3630, was delivered by the 101st Air Refueling Wing to the 309th Aerospace Maintenance and Regeneration Group at Davis–Monthan Air Force Base for long-term storage.
2009: Over 50 Years of Continuous Service
As of 2009, the KC-135 is one of a few military aircraft types with over 50 years of continuous service with its original operator.
February 2010: USAF Restarted KC-X Competition
In February 2010, the USAF restarted the KC-X competition with the release of a revised RFP.
February 2011: USAF Selected Boeing's Tanker Design
In February 2011, after evaluating bids, the USAF selected Boeing's 767-based tanker design as a replacement, with the military designation KC-46.
2013: Flight Hours of KC-135 57-1419
As of 2013, KC-135 57-1419 had 22,300 flight hours.
2013: Israel Offered KC-135s Again
In 2013, Israel was offered KC-135s again, after previously declining them twice due to the expense of maintenance. The IAF rejected the KC-135Es but expressed interest in up to a dozen of the newer KC-135Rs.
January 2017: Block 45 Program Delivery
By January 2017, the first 45 upgraded aircraft from the Block 45 program were delivered. Block 45 added a new glass cockpit digital display, radio altimeter, digital autopilot, digital flight director, and computer updates to the KC-135.
2017: Estimated Cost of Fleet Operations
KC-135 fleet operations and support costs were estimated to grow from about $2.2 billion in fiscal year 2003 to $5.1 billion (2003 dollars) in fiscal year 2017, an increase over 130%.
May 2018: AMC Managed Stratotankers
As of May 2018, AMC managed 396 Stratotankers, of which the AFR and ANG flew 243 in support of AMC's mission.
2018: Requirement for Skin Replacement
In March 2009, the Air Force indicated that KC-135s would require additional skin replacement to allow their continued use beyond 2018.
January 2019: First KC-46A Pegasus Delivered
In January 2019, the first KC-46A Pegasus was delivered to the USAF.
2024: Equivalent KC-135 Fleet Operation and Support Costs in 2024
The $2.2 billion KC-135 fleet operation and support cost in fiscal year 2001, is equivalent to about $3.71 billion in 2024.
February 2026: KC-135 Support During Operation Epic Fury
On 28 February 2026, a KC-135 provided aerial refueling support during Operation Epic Fury, a large-scale, joint US-Israeli military operation against Iran.
March 2026: KC-135 Crash in Iraq
On 12 March 2026, a KC-135 crashed in western Iraq, resulting in the death of all six crew members. The crash is thought to be the result of an incident involving another aerial refuelling aircraft.
2030: Projected Use of Upgraded KC-135Es
A 2005 USAF study estimated that KC-135Es upgraded to the R standard could remain in use until 2030.
2030: Projected Service Life
Studies concluded that many KC-135 aircraft could continue flying until 2030, although maintenance costs had significantly increased.
2040: Projected Lifetime of KC-135 Aircraft
The USAF projected that E and R models have lifetime flying hour limits of 36,000 and 39,000 hours, respectively. Accordingly, only a few KC-135s would reach these limits by 2040, when some aircraft would be about 80 years old.
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