KC-135 Stratotanker

Product Type:

Military Airlift/Aerial Refueling Aircraft (KC-135)
Military Special Mission Aircraft (RC-135/WC-135/OC-135)

Using Service (US):

Air Force (USAF)

Program Status:

No more new aircraft will be procured.
Focus is on upgrades and sustainment.

Prime Contractor:

The Boeing Company

The KC-135 Stratotanker

About the C-135 Family:

The Boeing KC-135 is a long range cargo, passenger airlift, and aerial refueling aircraft (+military special missions (RC-135)). In its latest configuration, the aircraft is powered by four CFM International CFM56-2B1 (F108) high-bypass turbofan engines, each providing 21,634 pounds of thrust. The Boeing model 367-80 jet transport and tanker prototype was the basic design for the commercial 707 passenger plane as well as the KC-135A Stratotanker. Built in Renton, WA, out of a total of 820 C-135s built, 732 were KC-135As, 17 were KC-135Bs, 45 aircraft were built as C-135A or C-135B "Stratolifter" transport aircraft without onboard tanker equipment (no longer in service), and another 14 aircraft were built and configured for military special missions (some of these are still in service - more info later in this article). The remaining 12 aircraft were C-135F Stratotankers built for the French Air Force. The KC-135 was purchased to replace U.S. Air Force KB-29, KB-50 and KC-97 four-engine, propeller-driven aircraft.

The KC-135 Stratotanker variant provides aerial refueling. Nearly all internal fuel can be pumped through the flying boom, which is the KC-135's primary fuel transfer method. A special drogue attached to and trailing behind the flying boom, may be used to refuel aircraft fitted with probes. Some KC-135s have been configured with the Multipoint Refueling System or MPRS. MPRS configured aircraft are capable of refueling two receiver aircraft simultaneously from special pods mounted on the wingtips.

On the KC-135, 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 83,000 pounds (37,650 kg) of cargo or six standard 463L pallets or 37 passengers. The KC-135 is also capable of transporting litter and ambulatory patients using patient support pallets during aeromedical evacuations. In 1954, the U.S. Air Force purchased the first 29 of its future fleet of 749 KC-135A/B aircraft. The first aircraft flew on August 31, 1956 and the initial production Stratotanker was delivered to Castle Air Force Base in California in June 1957. The last KC-135 was delivered to the Air Force in January 1966. The KC-135 fleet will be replaced by the Boeing KC-46 Pegasus (KC-X New Tanker). Deliveries will start in 2017 and KC-135 Stratotankers will gradually be retired as KC-46 aircraft arrive.

Of the original KC-135As (powered by Pratt & Whitney J57 turbojets), more than 415 were upgraded with new CFM56 engines from CFM-International. The re-engined tanker, designated KC-135R or KC-135T, can offload 50% more fuel, is 25% more fuel efficient, costs 25% less to operate and is 96% quieter than the KC-135A. Under another re-engining program, tankers with Pratt & Whitney TF33-PW-102 engines were designated the KC-135E. In 2009, the last KC-135E was retired.

The KC-135R/T aircraft continue to undergo life-cycle upgrades to expand their capabilities and improve reliability. Among these are improved communications, navigation, auto-pilot and surveillance equipment to meet future civil air traffic control requirements. As of April 2014, there are 396 KC-135s in the Air Force inventory with an average age of 52 years with 26 years of service life remaining (projected service life of 2040). On February 21, 2013, after more than 50 years of service (delivered in 1962) and 22,500 flying hours, the first operational KC-135R Stratotanker was retired from service.

RC-135 Variants:

The U.S. Air Force Manned Reconnaissance Systems Program includes seventeen RC-135V/W RIVET JOINT, three RC-135S COBRA BALL, and two RC-135U COMBAT SENT aircraft. All RC-135 aircraft are part of the 55th Wing based at Offutt Air Force Base in Nebraska.

The RC-135V/W RIVET JOINT reconnaissance aircraft provides near real time on-scene intelligence collection, analysis and dissemination capabilities. The interior seats more than 30 people, including the cockpit crew, electronic warfare officers, intelligence operators and in-flight maintenance technicians. The Rivet Joint fleet of 17 aircraft was re-engined with CFM56 engines and features upgraded "glass cockpit" deck instrumentation and navigational systems. With the majority of RC-135 aircraft being RIVET JOINTs, as a result, it drives the integration and modification upgrade strategy for the RC-135 fleet. Therefore, the majority of DoD modification funds are directly related to the RIVET JOINT.

The RC-135U COMBAT SENT provides strategic electronic reconnaissance information to the President, Secretary of Defense, Department of Defense, and military commanders. The RC-135U locates and identifies foreign military land, naval and airborne radar signals, and collects and examines each system to provide strategic analysis for military commanders. The fleet (2 aircraft) has been re-engined with CFM56 engines.

The RC-135S COBRA BALL, an extensively modified C-135B, is a measurement and signal intelligence aircraft equipped with special electro-optical instruments designed to detect ballistic missiles at long range. The Cobra Ball monitors missile signals and tracks missiles during boost and re-entry phases.

An RC-135 Viability Assessment was conducted in 2007 and the results reported that despite their fleet average airframe age of 44 years and accumulated flight hours (38,000) as of FY 2007, the RC-135 will be able to continue to perform its intended operations until 2040.

WC-135 Variant:

The WC-135W CONSTANT PHOENIX is an atmospheric collection aircraft, which gathers particulate and gaseous effluents and debris from accessible regions of the atmosphere in support of the Limited Nuclear Test Ban Treaty of 1963. The aircraft is a modified C-135B or EC-135C platform powered by four Pratt & Whitney TF33 turbofans. The WC-135W played a significant role in tracking radioactive debris from the disaster at the Chernobyl nuclear power plant in the Soviet Union. The WC-135W fleet of two aircraft is based at Offutt Air Force Base in Nebraska.

OC-135 Variant:

The OC-135B OPEN SKIES observation aircraft supports the Open Skies Treaty and performs unarmed flights over participating countries. The aircraft is a modified WC-135B powered by four Pratt & Whitney TF33 turbofans. The aircraft's primary mission is to take pictures. Therefore, most of the installed equipment and systems provide direct support to the cameras. The interior seats 35 people, including the cockpit crew, aircraft maintenance crew, foreign country representatives, and crew members from the U.S. DoD Defense Threat Reduction Agency. The OC-135B fleet of two aircraft is based at Offutt Air Force Base in Nebraska.



Price/Unit Cost:

The KC-135 is no longer in production. In FY 1998 dollars, the unit cost was $39.6 million.


KC-135: To provide the core aerial refueling capability for the U.S. Air Force until replaced. RC-135/WC-135/OC-135: To perform military special missions. For more information, see above.

FY 2014 DoD Program:

FY 2014 provides $29.6 million for KC-135 modifications. The primary modification in FY 2014 is the Block 45 Program, which addresses obsolescence, reliability and maintainability issues currently experienced by the KC-135 Fleet. The modification includes a new Digital Flight Director (DFD), Digital Radar Altimeter (RA), Digital Autopilot (AP) and Electronic Engine Instrument Displays (EEID). The DFD replaces the existing obsolete analog flight director (high maintenance driver) and provides a fully integrated flight guidance system and at the same time provides improved capability. The RA replaces the existing obsolete AL-101 radio altimeter (high maintenance driver) with a new state of the art digital high mean time between failure (MTBF) RA. The digital AP replaces the current obsolete analog AP system. The EEID replaces the obsolete analog engine instruments. FY 2014 also provides $174.5 million in modification funds for RC-135 Series aircraft.

FY 2015 DoD Program:

FY 2015 provides $63.6 million for KC-135 modifications. The primary modifications in FY 2015 are Block 45, VHF Omni-Directional Radio (VOR)/Instrument Landing System (ILS) Antennae and Low Cost Modifications (LCMs)that address obsolescence and improve flight safety, reliability, and maintainability. For more information, click to see the FY 2015 Air Force KC-135 Budget.

FY 2015 also provides $152.8 million in modification funds for RC-135 Series aircraft. For more information, click to see the FY 2015 Air Force RC-135 Budget.

Source: U.S. Department of Defense (DoD) and The Boeing Company.

Specifications Armament DoD Spending FY2015 Budget

Last Update: October 23, 2014.

By Joakim Kasper Oestergaard Balle /// (jkasper@bga-aeroweb.com)

External Resources:

The Boeing Company: Boeing KC-135 Stratotanker

YouTube: Boeing KC-135 Stratotanker | YouTube Videos

Fact Sheet: Not Available

C-135 DoD Spending Charts:

DoD Spending on the KC-135 Stratotanker + RC-135/WC-135/OC-135 in FY 2011, FY 2012, FY 2013, FY 2014 and FY 2015
DoD Purchases of C-135 Series Aircraft in FY 2011, FY 2012, FY 2013, FY 2014 and FY 2015
Defense Budget Data

Go to Top

DoD Spending, Procurement and RDT&E: FY 2011/12/13 + Budget for FYs 2014 + 2015

DoD Defense Spending, Procurement, Modifications, Spares, and RDT&E for the KC-135 Stratotanker

Download Official DoD Budget Documentation:

Modification of KC-135 Aircraft (USAF) Modification of RC-135 Aircraft (USAF)
Spares and Repair Parts (USAF)

Aircraft Specifications: KC-135R/T Stratotanker

Go to Top

Primary Function: Aerial refueling and airlift
Prime Contractor: The Boeing Co.
Power Plant: 4x CFM International CFM56-2B1 high-bypass turbofan engines
Thrust: 21,634 pounds (each engine)
Wingspan: 130 ft 10 in (39.9 m)
Length: 136 ft 3 in (41.5 m)
Height: 41 ft 8 in (12.7 m)
Weight (Empty): 98,500 lbs (44,700 kg)
Maximum Takeoff Weight (MTOW): 322,500 lbs (146,300 kg)
Maximum Transfer Fuel Load: 200,000 lbs (90,700 kg)
Capacity: 83,000 lbs (37,650 kg) of cargo or 37 passengers
Pallet Positions: 6 standard 463-L pallets
Speed: 461 kts/530 mph (853 km/h) at 30,000 ft (9,140 m)
Rate of Climb: 4,900 ft/min (24.89 m/s)
Service Ceiling: 50,000 ft (15,240 m)
Range: 1,303 nm/1,500 miles (2,400 km) with 150,000 lbs (68,000 kg) of transfer fuel;
Ferry: up to 9,570 nm/11,000 miles (17,700 km)
Crew: Three (pilot, co-pilot and boom operator). Some KC-135 missions require the addition of a navigator.
The Air Force has a limited number of navigator suites that can be installed for unique missions.
Aeromedical Evacuation Crew: A basic crew of five (two flight nurses and three medical technicians)
is added for aeromedical evacuation missions. Medical crew may be altered as required by the needs of patients.
Price/Unit Cost: $39.6 million (FY 1998 constant dollars)
First Flight: KC-135A: August 31, 1956; Prototype 367-80: July 15, 1954
Inventory: Total: 361 KC-135R and 54 KC-135T (as of September 2012) [400 total (as of April 2014)]
Active: 138 KC-135R and 30 KC-135T; ANG: 156 KC-135R and 24 KC-135T; Reserve: 67 KC-135R

Defense Program

Aircraft Programs Missile Programs Space Programs Shipbuilding Programs Vehicle Programs