An Unconventionally Classic Warbird

So just what is a classic warbird?  Is it defined by a certain amount of longevity – say 50 years ?  How many follow-on versions does an airframe need to prove its adaptability and durability – about three dozen?  What about its importance in shaping a nation’s combat doctrine and foreign policies by allowing worldwide power projection?  I’m not sure that there’s any one set of definitive rules which constitute a classic warbird, but I’m prepared to offer some answers for these and other questions to support my assertion that Boeing’s EC/RC/VC/NC/JKC/NKC/C/WC/OC/TC/KC-135 Stratotanker indeed is a classic warbird.

Boeing’s original Stratotanker design came from the Model 367-80 (otherwise known as the “Dash 80″), which first flew in 1954.  From this aircraft’s concept, separate paths emerged… the Boeing 707 (civil) and 717 (military).  That same year,  the U.S. Air Force’s Strategic Air Command (SAC) announced a competition for an aerial tanker companion for its new B-52 Stratofortress bomber.  Since Boeing projected that it could quickly field much needed tankers well ahead of any of its competitors (it already had a flyable prototype in the Dash 80), an interim contract of 117 newly-designated KC-135A Stratotankers was signed before the competition ended.  The first flight of the KC-135A occurred in August of 1956, and SAC received their first KC-135A nine months later.  Although this seems like a fast turnaround time, one cannot forget that much research and development had already been accomplished by the parallel 707 program.  Boeing actually lost the competition, but because the KC-135 had already begun operations, standardization won out and it ultimately garnered all the tanker orders, replacing the piston-engine KC-97s in service.

Eventually, 732 KC-135A tankers were delivered, plus 88 other C-135 airframes that were similar to the tanker, but with alternate equipment replacing the air refueling apparatus.  The last C-135 was delivered in 1965.  Close to three dozen variations on the theme of the original KC-135A have been produced, and this short look at many of them will be grouped into five categories: Tankers, Transports, Reconnaissance, Test and Evaluation, and Command and Control.

 

Tankers

The KC-135A was the front line jet tanker of the Air Force from the late 1950s through the early 1990s.  Similar to the -A were the 56 KC-135Qs, which were modified for refueling SR-71 Blackbirds (and the earlier CIA-operated A-12 too).  SAC depended on the tanker to make up part of their manned strategic nuclear deterrent  weapon, teamed with bombers that needed extended range to be able to reach targets in Russia.  KC-135s were an important tactical asset during the Vietnam War, providing fuel for conventionally armed B-52 bombers and tactical fighters.  The Air Force Reserve and Air National Guard began receiving KC-135As in 1975. From Vietnam through Desert Shield the KC-135A and -Q tankers enabled hundreds of safe aircrew and aircraft recoveries that could have ended in disaster without additional fuel.  The aircraft’s refueling capabilities enabled extended flight operations of aircraft on crisis and humanitarian missions worldwide too.

The KC-135A had its share of “bugs” and “squawks” as it came into operation in the late 1950s and 1960s.  The original Pratt and Whitney J-57-P-59W jet engines were marginally powerful enough to lift the tanker at full (more than 290,000 pounds) gross weight.  A system of demineralized water injection into the engines produced an extra 3,000 pounds of thrust for takeoff; the 670 gallons would be exhausted in some 2 1/2 minutes and produced a characteristic dark exhaust and plenty of noise when used.  If the water injection system malfunctioned during takeoff in certain configurations,  the aircraft didn’t have enough power to climb, and disastrous results could occur.    This problem wasn’t corrected until re-engining programs began years after the last tanker was delivered.  Structural fatigue problems in the rear fuselage caused mainly from sonic engine noise and certain flight maneuvers resulted in placing strengthening “strips” on the rear of the KC-135s.  The original short vertical tail fin was replaced with a taller version for better maneuverability.  Five aircraft were probably lost because of an aft body fuel  tank pump, which overheated when in operation while its tank was empty and caused vapors to explode.  A procedure was developed to keep 3,000 pounds of fuel in the tank to keep the motor cool.

The engine issues were solved by parallel programs that re-engined the KC-135 fleet.  The KC-135E was an -A model modified with a quartet of more powerful Pratt and Whitney TF-33-PW-102 turbofan engines with thrust reversers, new horizontal stabilizers from retired “donor” 707s, and new cockpit instruments and braking system.  The -E variant was 14% more fuel efficient and could offload 20% more fuel than the earlier -A and -Q series.  Importantly, it was 60% quieter to operate.  One hundred and sixty one KC-135Es were produced and operated by Air National Guard and Air Force Reserve units.  The last KC-135Es were retired in 2009.

The larger program to re-engine the older KC-135As and -Qs used F-108 turbofans, an adaption of the civilian CFM-56 engine.  The modified KC-135A became known as KC-135R and the -Qs became known as the KC-135T.  These aircraft offered huge improvements for the tanker fleet… with an 50% greater fuel offload, 25% better fuel efficiency in flight, costing 25% less to operate than an -A version, and is 90% quieter than the -A too.  In fact, two KC-135Rs can do the work of three KC-135As.  Ultimately, 414 KC-135As, -Es, and -Qs were modified into KC-135Rs and -Ts.  With the passing of SAC in 1992, ownership of the KC-135 tanker fleet was transferred to the Air Force’s Air Mobility Command.    Today, active duty Air Force (167), Air Force Reserve (67), and Air National Guard (180) units share the fleet.  Besides aerial refueling, the KC-135R can still carry cargo, and can be configured for the medical evacuation role with five additional crew in the rear to care for patients riding in litters.

Many of the oldest KC-135As were sent to storage in Tucson’s AMARC yard as re-engined aircraft improved efficiencies and the retirement of many Cold War aircraft resulted in excess capacity.   The United States was the original customer for the KC-135, but France bought a dozen KC-135F versions, which were basically -A aircraft with different systems.  These went on to be re-engined with CFM-56 engines too, and today are called KC-135FRs,  Chile, Turkey and Singapore also operate KC-135R tankers, which were drawn out of the stored aircraft, overhauled, and re-engined before being sold.

An important update of the KC-135E/R fleet was initiated in 1992, and ran from 1996 through 2002.  Pacer CRAG (Compass,  Radar, And GPS) updated cockpit instruments with glass displays and capabilities to operate in future global air traffic management airspace.  This capability produced a major change within the Stratotanker’s crew; the navigator was dropped as advanced navigation equipment made the position redundant.  This program put the KC-135R on track to fly until the year 2040.

Of the 88 airframes that were produced for specialized roles, less than three dozen soldier on in reconnaissance and training roles today.  Later versions of the larger Boeing 707-300 Intercontinental variant earned a new designation in Air Force service as either the C-18 or C-137 and were not a KC-135 variant.  The E-3 AWACS and E-8 Joint STARS aircraft are based on the -300’s larger design too.

 

Transport

The Air Force ordered several C-135s without refueling gear, with accommodations for up to 160 troops or nine pallets of cargo.  These offered a high speed transport capability unmatched until the arrival of the C-141 Starlifter years later.  The C-135A used J-57 engines, while the C-135B used TF-33 turbofans with greatly improved thrust.  Several C-135C aircraft were built too; some of each version were converted into VIP transports as VC-135As and VC-135Bs.  After their initial transport role was completed, the C-135 fleet were converted into several different variants for different missions.

 

Reconnaissance

C-135s became important  American spies in the sky due to their long range, high speed, and large capacity for specialized equipment.  A myriad of special designations have been bestowed on different models, and many are known better by their system names rather than their type designators.  Most remaining types in current use have been modified from C-135A/B airframes and have gone through the Pacer CRAG and F108 re-engining upgrades.

The RC-135S Cobra Ball specializes in electro optical reconnaissance.  They are readily identified by a series of circular windows on the right side of the fuselage, and the flat black paint of the right wing that reduces solar glare that degrades sensor operation.  A training airframe is known as the TC-135S.  The remaining pair of RC-135U Combat Sent  aircraft are configured to make precise measurements of radio transmitters.  There are 17 RC-135V and RC-135W Rivet Joint aircraft, which collect and distribute information from across the “electromagnetic” spectrum, according to the Air Force.   These are easily recognizable due to their sensor “cheeks” and “hog nose” modifications.  A TC-135W trainer jet used to keep operational aircraft freed up to perform their mission.  The Air Force operates an OC-135B and OC-135W aircraft for the compliance of the 2002 Open Skies Treaty.  There is one WC-135W Constant Phoenix weather reconnaissance jet too; this is used for atmospheric detection and collection of particles from nuclear testing.  The WC-135W was deployed to Alaska for sampling flights after the 2011 tsunami that crippled the Japanese Fukushima nuclear power plant.

 

Test and Evaluation

Any aircraft with an -N or -J suffix attached to it identifies a test aircraft… often times modified significantly from its primary role.  There were many NKC-135A, NKC-135E, and JKC-135A  aircraft that were modified to test systems and measure experiment results.  Many of these aircraft were based at Wright Patterson and Edwards AFBs, although there are few if any left in service.

 

Command and Control

The “Looking Glass” was an airborne command post capable of relaying information for launching an attack if of a nuclear war occurred.   The mission provided at least one airborne aircraft continuously from February 3, 1960 through July 24, 1990.  Airborne command post C-135s that shared the Looking Glass duties included the EC-135C, EC-135A, ECO-135A, and EC-135J.  One of many models used for different specialized command and control duties included the EC-135K Head Dancer aircraft, required for complex “fighter drags” across the Atlantic and Pacific oceans between the U.S and Europe and Asia.  A telemetry and communications relay model, known as the EC-135N Apollo/Advanced Range and Instrumentation aircraft (ARIA) were identified by their large bulbous nose fairing.

Few other weapons systems can match the KC-135’s longevity (56 years) and utility in Air Force use.   Other models in use for more than 50 years include the B-52, C-130, T-38, U-2 and F-4… some great company indeed.  Many variants of the KC-135 have come and gone, their jobs either disappearing in an ever changing world, or taken on by younger aircraft.  The tanker duties haven’t gone away though, and the KC-135’s successors won’t totally replace it soon.  By proving its longevity, its adaptability for a wide range of missions, and its value to the Air Force, I think the KC-135 (and its variants) have indeed proven to be a classic aircraft design.

 

Ken Kula

(Photo by the author unless otherwise credited)

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