Boeing KC-135 Stratotanker

Summary

Description

The KC-135 Stratotanker is an American military aerial refueling aircraft developed by Boeing. The aircraft was first introduced into service in 1957 as a part of the United States Air Force's Strategic Air Command. It was initially designed to refuel strategic bombers like the B-52 Stratofortress but has since evolved to serve a variety of roles, including cargo transport and personnel airlift.

The KC-135 was developed to replace older refueling aircraft like the KB-29 and KB-50 and was the first jet-powered refueling tanker in the U.S. military. It was born out of the need for a dedicated, fast, and high-altitude tanker capable of keeping up with the latest generation of jet bombers and fighters.

The aircraft is based on the Boeing 367-80, commonly known as the "Dash 80," which was itself a prototype for both the Boeing 707 airliner and the KC-135. The development of the KC-135 was expedited given the Cold War context, where the ability to keep strategic bombers in the air for extended periods was considered crucial for nuclear deterrence.

The development and design of the KC-135 Stratotanker were deeply influenced by the requirements of the Cold War era. Speed and altitude capabilities were primary considerations, as the aircraft was initially intended to refuel strategic bombers like the B-52, which operated at higher altitudes and speeds than earlier propeller-driven bombers. The KC-135 was conceived to be jet-powered from the outset, providing it with the necessary speed and altitude performance to meet these operational demands.

The aircraft is derived from Boeing's 367-80 prototype, also known as the "Dash 80." While the Dash 80 served as a proof of concept for both commercial and military jet aviation, specific modifications were made to meet the Air Force’s requirements for the KC-135. Unlike its commercial cousin, the Boeing 707, the KC-135 has a narrower fuselage and is shorter in length, designed specifically for its mission as a tanker.

One of the key design elements of the KC-135 is its flying boom, which serves as the primary method of transferring fuel to receiver aircraft. Operated by a boom operator stationed at the rear of the plane, the flying boom can be extended and inserted into a receptacle on the receiving aircraft, enabling the high-speed transfer of fuel. This system was revolutionary at the time of its introduction and provided a much more efficient and faster refueling process compared to older hose-and-drogue methods.

Structurally, the KC-135 was engineered with longevity in mind. It features a predominantly aluminum airframe and a conventional swept-wing design. Notable updates include re-engining programs that replaced the original turbojet engines with more efficient turbofan engines, avionic upgrades for better navigation and communication, and enhancements to its fuel transfer systems.

Operational history

The KC-135 Stratotanker has a long and storied operational history, having been in continuous service with the United States Air Force since 1957. Initially conceived during the Cold War to refuel strategic bombers like the B-52 Stratofortress, the aircraft was a cornerstone of the U.S. strategy of nuclear deterrence. Its ability to extend the range and endurance of these bombers was critical in providing the U.S. with a credible second-strike capability.

Beyond the Cold War, the KC-135 has played a significant role in nearly every American military engagement since its introduction. During the Vietnam War, it supported B-52 bombing missions and tactical fighters operating over North and South Vietnam. In the Gulf War of 1990-1991, KC-135s were essential in enabling the long-range strikes that helped quickly incapacitate Iraqi forces. They were also critical in the Afghanistan and Iraq wars in the early 2000s, supporting round-the-clock air operations over both countries.

The KC-135 has not been limited to combat operations. It has been used for humanitarian missions, including disaster relief and medical evacuations. It's also been involved in various special-purpose adaptations and missions, such as reconnaissance, electronic warfare, and even as a zero-gravity training platform for astronauts.

Given its long service life, the aircraft has gone through multiple upgrades and modifications. The most significant of these was the re-engining program that replaced the original J-57 turbojets with more efficient CFM56 turbofan engines. This not only improved the KC-135's fuel efficiency but also extended its operational lifespan.

Variants

The KC-135 Stratotanker has seen various modifications and adaptations:

• KC-135A: The original version, fitted with Pratt & Whitney J-57 turbojet engines. These were later re-engined with more efficient CFM56 turbofan engines to become KC-135E and KC-135R variants.
• KC-135B: A specialized version designed for electronic intelligence (ELINT) missions, these were later reconfigured back into the standard tanker role.
• KC-135D: These were converted from RC-135Ds and were intended for refueling fighter aircraft deployed to the Pacific region.
• KC-135R: The most numerous variant in service today, these are KC-135As and KC-135Es re-engined with CFM International CFM56 (military designation: F108) turbofan engines, providing greater fuel efficiency and thrust.
• EC-135: A variant equipped for airborne command post missions, various sub-variants exist with different types of mission equipment.
• RC-135: A reconnaissance version of the KC-135, with multiple subtypes designed for electronic intelligence gathering, signals intelligence, and other specialized reconnaissance tasks.
• WC-135: Known as the "Constant Phoenix," this variant is used for collecting samples from the atmosphere to detect and identify nuclear explosions.
• OC-135: Specifically modified for the Open Skies Treaty, these are used for unarmed observation flights over treaty countries to monitor military activities.

Technical specifications

Current operating countries

Country		Units
	United States	388
	France	10
	Turkey	7
	Chile	3

Numbers in parentheses, e.g. '(+5)', indicate units ordered but not yet delivered.

All operators

Australia • Brazil • Chile • Spain • France • Israel • Italy • Morocco • Singapore • Turkey • United States • Venezuela • South Africa

Photo of KC-135 Stratotanker

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