Boeing-Hayes KB-50J "Superfortress"
United States — USAF four-engine tanker

Archive Photos

Boeing KB-50J "Superfortress" (AF 48-114) at the National Museum of the United States Air Force, Wright Patterson Air Force Base, Dayton, Ohio (Photos by John Shupek)

Overview 2

Boeing B-50 Superfortress

The Boeing B-50 Superfortress is an American strategic bomber. A post-World War II revision of the Boeing B-29 Superfortress, it was fitted with more powerful Pratt & Whitney R-4360 radial engines, stronger structure, a taller tail fin, and other improvements. It was the last piston-engined bomber designed by Boeing for the United States Air Force (except the never-completed B-54, a derivative of the B-50). Not as well known as its direct predecessor, the B-50 was in USAF service for nearly 20 years.

After its primary service with SAC ended, B-50 airframes were modified into aerial tankers for Tactical Air Command (KB-50) and as weather reconnaissance aircraft (WB-50) for the Air Weather Service. Both the tanker and hurricane hunter versions were retired in March 1965 due to metal fatigue and corrosion found in the wreckage of KB-50J, 48-065, which crashed on 14 October 1964.

Design and Development 2

Development of an improved B-29 started in 1944, with the desire to replace the unreliable Wright R-3350 Duplex Cyclone engines with the more powerful four-row, 28-cylinder Pratt & Whitney R-4360 Wasp Major radial engine, America’s largest-ever displacement aircraft piston engine in large-scale production. A B-29A-5-BN (AF 42-93845) was modified by Pratt & Whitney as a testbed for the installation of the R-4360 in the B-29, with four 3,000 hp (2,200 kW) R-4360-33s replacing the 2,200 hp (1,600 kW) R-3350s. The modified aircraft, designated XB-44 Superfortress, first flew in May 1945. The planned Wasp-Major powered bomber, the B-29D, was to incorporate considerable changes in addition to the engine installation tested in the XB-44. The use of a new alloy of aluminum, 75-S rather than the existing 24ST, gave a wing that was both stronger and lighter, while the undercarriage was strengthened to allow the aircraft to operate at weights of up to 40,000 lb (18,000 kg) greater than the B-29. A larger vertical fin and rudder (which could fold to allow the aircraft to fit into existing hangars) and enlarged flaps were provided to deal with the increased weight. Armament was similar to that of the B-29, with two bomb bays carrying 20,000 lb (9,100 kg) of bombs, and a further 8,000 lb (3,600 kg) externally. Defensive armament was 13 × .50 in (12.7 mm) machine guns (or 12 machine guns and one 20mm cannon) in five turrets.

First flying in May 1945, the sole XB-44 proved 50-60 mph (80-97 km/h) faster than the standard B-29, although existing sources do not indicate how much of this increased speed was due to differing aircraft weight due to deleted armament or increased power due to the R-4360-33 engines.

An order for 200 B-29Ds was placed in July 1945, but the ending of World War II in August 1945 prompted mass cancellations of outstanding orders for military equipment, with over 5,000 B-29s canceled in September 1945. In December that year, B-29D orders were cut from 200 to 60, while at the same time the designation of the aircraft was changed to B-50.

Officially, the aircraft’s new designation was justified by the changes incorporated into the revised aircraft, but according to Peter M. Bowers, a long-time Boeing employee and aircraft designer, and a well-known authority on Boeing aircraft, "the re-designation was an outright military ruse to win appropriations for the procurement of an airplane that by its B-29D designation appeared to be merely a later version of an existing model that was being canceled wholesale, with many existing examples being put into dead storage."

The first production B-50A (there were no prototypes, as the aircraft’s engines and new tail had already been tested) made its maiden flight on 25 June 1947, with a further 78 B-50As following. The last airframe of the initial order was held back for modification to the prototype YB-50C, a planned version to be powered by R-4360-43 turbo-compound engines. It was to have a longer fuselage, allowing the two small bomb bays of the B-29 and the B-50A to be replaced by a single large bomb bay, more suited to carrying large nuclear weapons. It would also have longer span wings, which required additional outrigger wheels to stabilize the aircraft on the ground. Orders for 43 B-54s, the planned production version of the YB-50C, were placed in 1948, but the program was unpopular with Curtis LeMay, commander of Strategic Air Command (SAC), as being inferior to the Convair B-36 and having little capacity for further improvement, while requiring an expensive redevelopment of air bases owing to the type’s undercarriage. The B-54 program was therefore canceled in April 1949, work on the YB-50C being stopped prior to it being completed.

While the B-54 was canceled, production of less elaborate developments continued as a stopgap until jet bombers like the Boeing B-47 and B-52 could enter service. Forty-five B-50Bs, fitted with lightweight fuel tanks and capable of operating at higher weights, were built, followed by 222 B-50Ds, capable of carrying underwing fuel tanks and distinguished by a one-piece plastic nose dome. To give the Superfortress the range to reach the Soviet Union, B-50s were fitted to be refueled in flight. Most (but not all) of the B-50As were fitted with the early "looped hose" refueling system, developed by the British company Flight Refuelling Limited, in which the receiving aircraft would use a grapple to catch a line trailed by the tanker aircraft (normally a Boeing KB-29) before hauling over the fuel line to allow transfer of fuel to begin. While this system worked, it was clumsy, and Boeing designed the alternative Flying Boom method to refuel SAC’s bombers, with most B-50Ds being fitted with receptacles for Flying Boom refueling.

Revisions to the B-50 (from its predecessor B-29) would boost top speed to just under 400 mph (644 km/h). Changes included:

Redesigned with a large upper fuselage grafted on, the B-50 design would form the basis for the Boeing 377 series of airliners and C-97/KC-97 military transports, with 816 of the KC-97 built. The B-29 and B-50 were phased out with introduction of the jet-powered B-47 Stratojet. The B-50 was nicknamed "Andy Gump" because the redesigned engine nacelles reminded aircrew of the chinless newspaper comic character popular at the time.

Operational History 2

Boeing built 370 of the various B-50 models and variants between 1947 and 1953, the tanker and weather reconnaissance versions remaining in service until 1965.

The first B-50As were delivered in June 1948 to the Strategic Air Command’s 43d Bombardment Wing, based at Davis-Monthan AFB, Arizona. The 2d Bombardment Wing at Chatham AFB, Georgia also received B-50As; the 93d Bombardment Wing at Castle AFB, California and the 509th Bombardment Wing at Walker AFB, New Mexico received B-50Ds in 1949. The fifth and last SAC wing to receive B-50Ds was the 97th Bombardment Wing at Biggs AFB, Texas in December 1950.

The mission of these wings was to be nuclear-capable and, in wartime, be able to deliver the atomic bomb on enemy targets if ordered by the president.

The 301st Bombardment Wing at MacDill AFB, Florida received some B-50As reassigned from Davis-Monthan in early 1951, but used them for non-operational training pending the delivery of B-47A Stratojets in June 1951. The B-50 was built as an interim strategic bomber to be replaced by the B-47 Stratojet, but delays to the Stratojet forced the B-50 to soldier on until well into the 1950s.

A strategic reconnaissance version of the B-50B, the RB-50 was developed in 1949 to replace the aging RB-29s used by SAC in its intelligence gathering operations against the Soviet Union. There were three different configurations produced, which were later redesignated RB-50E, RB-50F, and RG-50G respectively. The RB-50E was earmarked for photographic reconnaissance and observation missions; The RB-50F resembled the RB-50E but carried the SHORAN radar navigation system designed to conduct mapping, charting, and geodetic surveys, and the mission of the RB-50G was electronic reconnaissance. These aircraft were operated primarily by the 55th Strategic Reconnaissance Wing. RB-50Es were also operated by the 91st Strategic Reconnaissance Wing as a replacement for RB-29 photographic reconnaissance aircraft flown over North Korea during the Korean War.

The vast northern borders of the Soviet Union were wide open in many places during the early Cold War years with little defensive radar coverage, with limited detection capability. RB-50 aircraft of the 55th SRW flew many sorties along the periphery, and where necessary into the interior. Initially, there was little opposition from the Soviet forces as radar coverage was limited and, if the overflying aircraft were detected, the World War II era Soviet fighters could not intercept the RB-50s at their high altitude.

The deployment of the MiG-15 interceptor in the early 1950s made these flights exceedingly hazardous, with several being shot down by Soviet air defenses and the wreckage being examined by intelligence personnel. RB-50 missions over Soviet territory ended by 1954, replaced by RB-47 Stratojet intelligence aircraft that could fly higher near supersonic speed.

The B-47 Stratojet was manufactured in large numbers beginning in 1953 and eventually replaced the B-50Ds in SAC service; the last being retired in 1955. With its retirement from the nuclear-bomber mission, many B-50 airframes were converted to aerial refueling tankers.

The B-50, with more powerful engines than the KB-29s in use by Tactical Air Command, was much more suitable to refuel tactical jet fighter aircraft, such as the F-100 Super Sabre. As tankers, KB-50s would feature extensively reinforced outer wing panels, the necessary equipment to air refuel simultaneously three fighter-type aircraft by the probe and drogue method, and removal of defensive armament.

The first KB-50 flew in December 1955 and was accepted by the Air Force in January 1956. The tankers steadily entered the operational inventory of Tactical Air Command (TAC) supplanting TACs KB-29s. By the end of 1957, all of the command’s aerial refueling squadrons had their full complement of KB-50s. KB-50s, and later KB-50Js with two General Electric J47 jet engines were used by TAC, and also by USAFE and PACAF overseas as aerial tankers. Some were deployed to Thailand and flew refueling missions over Indochina in the early years of the Vietnam War until being retired in March 1965 due to metal fatigue and corrosion.

In addition to the aerial tanker conversion, the Air Weather Service by 1955 had basically worn out the WB-29s used for hurricane hunting and other weather reconnaissance missions. Thirty-six former SAC B-50Ds were stripped of their armament and equipped for long-range weather reconnaissance missions. The WB-50 could fly higher and faster and longer than the WB-29. However, between 1956 and 1960 it experienced 13 major operational accidents, six of them involving the loss of the entire crew, and 66 crew member fatalities. After the weather reconnaissance fleet was grounded in May 1960 because of fuel leaks, plans were set in motion in 1962 to modify Boeing B-47 Stratojets being phased out of SAC to replace it in the role. The WB-50 had an important role during the Cuban Missile Crisis, when it monitored the weather around Cuba to plan photo-reconnaissance flights. The WB-50 was also retired in 1965 due to metal fatigue and corrosion.

Variants 2

Boeing XB-44

One B-29A was handed over to Pratt & Whitney to be used as a testbed for the installation of the new Wasp Major 28-cylinder engines in the B-29.

Boeing B-29D

Wasp Major powered bomber, with stronger structure and taller tail. Redesignated B-50A in December 1945.

Boeing B-50A

First production version of the B-50. Four R-4360-35 Wasp Major engines, 168,500 lb (76,550 kg) max take-off weight. A total of 79 were built.

TB-50A - Conversion of 11 B-50As as crew trainers for units operating the Convair B-36.

Boeing B-50B

Improved version, with increased maximum take-off weight (170,400 lb (77,290 kg)) and new, lightweight fuel tanks. 45 built.

EB-50B - Single B-50B modified as test-bed for bicycle undercarriage, later used to test "caterpillar track" landing gear.

RB-50B - Conversion of B-50B for strategic reconnaissance, with capsule in rear fuselage carrying nine cameras in four stations, weather instruments, and extra crew. Could be fitted with two 700-US-gallon (2,650 L) drop tanks under outer wings. 44 converted from B-50B.

Boeing YB-50C

Prototype for B-54 bomber, to have Variable Discharge Turbine (i.e. turbo-compound) version of the R-4360 engine, longer fuselage and bigger, stronger wings. One prototype started but canceled before completion.

Boeing B-50D

Definitive bomber version of the B-50. Higher max takeoff weight of 173,000 lb (78,600 kg)). Fitted with receptacle for Flying boom in-flight refueling and provision for underwing drop tanks. Modified nose glazing with 7-piece nose cone window was replaced by a single plastic cone and a flat bomb-aimer’s window. A total of 222 were built.

Boeing DB-50D - Single B-50D converted as drone director conversion of a B-50D, for trials with the GAM-63 RASCAL missile.

Boeing KB-50D - Prototype conversion of two B-50Ds as three-point aerial refueling tanker, using drogue-type hoses. Used as the basis for later production KB-50J and KB-50K conversions. A further conversion from a TB-50D was also designated KB-50D.

Boeing TB-50D - Conversion of early B-50Ds lacking aerial-refueling receptacles as unarmed crew trainers. Eleven were converted.

Boeing WB-50D - Conversion of surplus B-50Ds as weather reconnaissance aircraft to replace worn out WB-29s. Fitted with doppler radar, atmospheric sampler and other specialist equipment, and extra fuel in the bomb bay. Some were used to carry out highly classified missions for atmospheric sampling from 1953-1955 to detect Soviet detonation of atomic weapons.

Boeing RB-50E

14 RB-50Bs converted at Wichita for specialist photographic reconnaissance.

Boeing RB-50F

Conversion of 14 RB-50Bs as survey aircraft, fitted with SHORAN navigation radar.

Boeing RB-50G

Conversion of the RB-50B for electronic reconnaissance. Fitted with Shoran for navigation, and six electronic stations, with 16-man crew; 15 converted.

Boeing TB-50H

Unarmed crew trainer for B-47 squadrons. 24 completed, the last B-50s built. All later converted to KB-50K tankers.

Boeing KB-50J

Conversions to air-to-air refueling tankers with improved performance from two extra General Electric J47 turbojets under the outer wings, 112 converted from B-50D, TB-50D, RB-50E, RB-50F and RB-50G aircraft.

Boeing KB-50

136 conversions to three point hose-drogue tankers by Hayes Industries, with the auxiliary fuel tanks outboard of the engines and hose pod under the wing-tips.

Boeing KB-50K

Tanker conversions of the TB-50H trainer aircraft. 24 converted.

Boeing B-54A

Proposed version of the YB-50C.

Boeing RB-54A

Proposed reconnaissance version of the YB-50C.

Boeing WB-50

Weather reconnaissance aircraft converted from B-50A aircraft.

Aircraft on Display 2

From the 370 produced only five B-50 aircraft survive today:

  1. Boeing B-50A: AF s/n 46-0010 ’Lucky Lady II’ - Flew around the world from 26 Feb-2 Mar 1949 non-stop. She was disassembled after a serious accident and her forward fuselage is stored outside at Planes of Fame in Chino, California.
  2. Boeing WB-50D: AF s/n 49-0310 - National Museum of the United States Air Force at Wright-Patterson Air Force Base in Dayton, Ohio.
  3. Boeing EB-50D: AF s/n 49-0351 ’Flight Of The Phoenix’ - Castle Air Museum at the former Castle Air Force Base in Atwater, California. This was the last B-50 to be flown, being delivered to MASDC at Davis-Monthan AFB, Arizona on 6 October 1965. She was put on display at the Castle Air Museum in 1980.
  4. Boeing KB-50J: AF Ser No. 49-0372 - Pima Air & Space Museum adjacent to Davis-Monthan Air Force Base in Tucson, Arizona.
  5. Boeing KB-50J: AF s/n 49-0389 - MacDill Memorial Park at MacDill Air Force Base in Tampa, Florida. Although accessible to active and reserve military personnel, military retirees and associated military family members, she is not accessible to the general public.

Operators - United States Air Force 2

Strategic Air Command

All Weather Service

Tactical Air Command

Boeing KB-50 Superfortress:

Boeing-Hayes KB-50J Stratotanker Specifications 3,4

General Characteristics


Weights and Loadings

Power Plants

Performance (basic mission)

Performance (max. refuel mission)

Performance (max. radius)


  1. Shupek, John. Photos via The Skytamer Archive, copyright © 2001 Skytamer Images. All Rights Reserved
  2. Wikipedia, the free encyclopedia. B-50 Superfortress
  3. Taylor, John W.R., "Hayes: The Hayes-Boeing KB-50J." Jane’s All The World’s Aircraft 1960-61. Jane’s All The World’s Aircraft Publishing Co. Ltd, London, 1960. pp. 321-322
  4. National Museum of the United States Air Force. "Fact Sheets: Boeing KB-50J Superfortress." [Online] Available, 8 December 2009


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