Boeing B-52 Stratofortress

The Boeing B-52 Stratofortress is a long-range, subsonic, jet-powered strategic bomber. The B-52 was designed and built by Boeing, which has continued to provide support and upgrades. It has been operated by the United States Air Force (USAF) since the 1950s. The bomber carries up to 70,000 pounds (32,000 kg) of weapons.^[4]
Beginning with the successful contract bid in June 1946, the B-52 design evolved from a straight-wing aircraft powered by six turboprop engines to the final prototype YB-52 with eight turbojet engines and swept wings. The B-52 took its maiden flight in April 1952. Built to carry nuclear weapons for Cold War-era deterrence missions, the B-52 Stratofortress replaced the Convair B-36. Although a veteran of several wars, the Stratofortress has dropped only conventional munitions in combat. Its Stratofortress name is rarely used outside official contexts; it has been referred to by Air Force personnel as the BUFF (Big Ugly Fat/Flying Fucker/Fellow).
The B-52 has been in active service with the USAF since 1955. As of 2012, 58 remain in service with nine in reserve. The bombers flew under the Strategic Air Command (SAC) until it was inactivated in 1992 and its aircraft absorbed into the Air Combat Command (ACC); in 2010 all B-52 Stratofortresses were transferred from the ACC to the new Air Force Global Strike Command (AFGSC). Superior performance at high subsonic speeds and relatively low operating costs have kept the B-52 in service despite the advent of later aircraft, including the canceled Mach 3 North American XB-70 Valkyrie, the variable-geometry Rockwell B-1B Lancer, and the stealth Northrop Grumman B-2 Spirit. The B-52 marked its 50th anniversary of continuous service with its original operator in 2005 and after being upgraded between 2013 and 2015 it will serve into the 2040s.^{[N 1]}

Origins

Models 462 (1946)^[9] to 464-35 (1948)^[9]

Models 464-49 (1949)^[9] to B-52A (1952)

On 23 November 1945, Air Materiel Command (AMC) issued desired performance characteristics for a new strategic bomber "capable of carrying out the strategic mission without dependence upon advanced and intermediate bases controlled by other countries".^[10] The aircraft was to have a crew of five or more turret gunners, and a six-man relief crew. It was required to cruise at 300 mph (240 knots, 480 km/h) at 34,000 feet (10,400 m) with a combat radius of 5,000 miles (4,300 nautical mile, 8,000 km). The armament was to consist of an unspecified number of 20 mm cannon and 10,000 pounds (4,500 kg) of bombs.^[11] On 13 February 1946, the Air Force issued bid invitations for these specifications, with Boeing, Consolidated Aircraft, and Glenn L. Martin Company submitting proposals.^[11]
On 5 June 1946, Boeing's Model 462, a straight-wing aircraft powered by six Wright T35 turboprops with a gross weight of 360,000 pounds (160,000 kg) and a combat radius of 3,110 miles (2,700 nmi, 5,010 km), was declared the winner.^[12] On 28 June 1946, Boeing was issued a letter of contract for US$1.7 million to build a full-scale mock-up of the new XB-52 and do preliminary engineering and testing.^[13] However, by October 1946, the Air Force began to express concern about the sheer size of the new aircraft and its inability to meet the specified design requirements.^[14] In response, Boeing produced Model 464, a smaller four-engine version with a 230,000 pound (105,000 kg) gross weight, which was briefly deemed acceptable.^[14][15]
Subsequently, in November 1946, the Deputy Chief of Air Staff for Research and Development, General Curtis LeMay, expressed the desire for a cruise speed of 400 miles per hour (345 kn, 645 km/h), to which Boeing responded with a 300,000 lb (136,000 kg) aircraft.^[16] In December 1946, Boeing was asked to change their design to a four-engine bomber with a top speed of 400 miles per hour, range of 12,000 miles (10,000 nmi, 19,300 km), and the ability to carry a nuclear weapon; in total, the aircraft could weigh up to 480,000 pounds (220,000 kg).^[17] Boeing responded with two models powered by the T-35 turboprops. The Model 464-16 was a "nuclear only" bomber with a 10,000 pound (4,500 kg) payload, while the Model 464-17 was a general purpose bomber with a 9,000 pound (4,000 kg) payload.^[17] Due to the cost associated with purchasing two specialized aircraft, the Air Force selected Model 464-17 with the understanding that it could be adapted for nuclear strikes.^[18]
In June 1947, the military requirements were updated and the Model 464-17 met all of them except for the range.^[19] It was becoming obvious to the Air Force that, even with the updated performance, the XB-52 would be obsolete by the time it entered production and would offer little improvement over the Convair B-36; as a result, the entire project was postponed for six months.^[20] During this time, Boeing continued to perfect the design which resulted in the Model 464-29 with a top speed of 455 miles per hour (395 kn, 730 km/h) and a 5,000-mile range.^[21] In September 1947, the Heavy Bombardment Committee was convened to ascertain performance requirements for a nuclear bomber. Formalized on 8 December 1947, these requirements called for a top speed of 500 miles per hour (440 kn, 800 km/h) and an 8,000 mile (7,000 nmi, 13,000 km) range, far beyond the capabilities of 464-29.^[20][22]
The outright cancellation of the Boeing contract on 11 December 1947 was staved off by a plea from its president William McPherson Allen to the Secretary of the Air Force Stuart Symington.^[23] Allen reasoned that the design was capable of being adapted to new aviation technology and more stringent requirements.^[24] In January 1948 Boeing was instructed to thoroughly explore recent technological innovations, including aerial refueling and the flying wing.^[25] Noting stability and control problems Northrop was experiencing with their YB-35 and YB-49 flying wing bombers, Boeing insisted on a conventional aircraft, and in April 1948 presented a US$30 million (US$287 million today^[26]) proposal for design, construction, and testing of two Model 464-35 prototypes.^[27] The Model 464-35 design bore similarity to a later Tupolev design that was built for the Soviet Union, the Tupolev Tu-95 Bear strategic bomber.^[28] Further revisions during 1948 resulted in an aircraft with a top speed of 513 miles per hour (445 kn, 825 km/h) at 35,000 feet (10,700 m), a range of 6,909 miles (6,005 nmi, 11,125 km), and a 280,000 pounds (125,000 kg) gross weight which included 10,000 pounds (4,500 kg) of bombs and 19,875 US gallons (75,225 L) of fuel.^[29][30]

Design effort

XB-52 Prototype on flight line (X-4 in foreground)

Side view of YB-52 bomber, with bubble canopy similar to that of the B-47

In May 1948, AMC asked Boeing to incorporate the previously discarded, but now more fuel-efficient, jet engine into the design.^[31] This resulted in Boeing developing yet another revision – in July 1948, Model 464-40 substituted Westinghouse J40 turbojets for the turboprops.^[32] The Boeing engineers took the Model 464-40 study to the Air Force Project Officer, and he was favorably impressed, especially since he had already been thinking along similar lines. Nevertheless, the government was still concerned about the high fuel consumption rate of the jet engines of the day, and directed that Boeing still use the turboprop-powered Model 464-35 as the basis for the XB-52. Although he agreed that turbojet propulsion was the future, General Howard A. Craig, Deputy Chief of Staff for Material, was not very keen on a jet-powered B-52, since he felt that the jet engine had still not progressed sufficiently to permit skipping an intermediate turboprop stage. However, Boeing was encouraged to continue with turbojet studies even though no commitment to jet propulsion could be expected.^[33][34]
On Thursday, 21 October 1948, Boeing engineers George S. Schairer, Art Carlsen and Vaughn Blumenthal presented the design of a four-engine turboprop bomber to the Air Force chief of bomber development, Col. Pete Warden. Warden was disappointed by the projected aircraft and asked if the Boeing team could come up with a proposal for a four-engine turbojet bomber. Joined by Ed Wells, Boeing vice president of Engineering, the engineers worked that night in the Hotel Van Cleve redesigning Boeing's proposal as a four-engine turbojet bomber. On Friday, Col. Warden looked over the information and asked for a better design. Returning to the hotel, the Boeing team was joined by Bob Withington and Maynard Pennell, two top Boeing engineers who were in town on other business.^[35]
By late Friday night, they had laid out what was essentially a new airplane. The new design (464-49) built upon the basic layout of the B-47 Stratojet with 35 degree swept wings, eight engines paired in four underwing pods, and bicycle landing gear with wingtip outrigger wheels.^[36] A notable feature of the landing gear was the ability to pivot the main landing gear up to 20° from the aircraft centerline to increase safety during crosswind landings.^[37] After a trip to a hobby shop for supplies, Schairer set to work building a model. The rest of the team focused on weight and performance data. Wells, who was also a skilled artist, completed the aircraft drawings. On Sunday, a stenographer was hired to type a clean copy of the proposal. On Monday, Schairer presented Col. Warden with a neatly bound 33-page proposal and a 14-inch scale model.^[35] The aircraft was projected to exceed all design specifications.^[38]
Although the full-size mock-up inspection in April 1949 was generally favorable, range again became a concern since the J40s and early model J57s had excessive fuel consumption.^[39] Despite talk of another revision of specifications or even a full design competition among aircraft manufacturers, General LeMay, now in charge of Strategic Air Command, insisted that performance should not be compromised due to delays in engine development.^[40][41] In a final attempt to increase range, Boeing created the larger 464-67, stating that once in production, the range could be further increased in subsequent modifications.^[42] Following several direct interventions by LeMay,^[43] Boeing was awarded a production contract for 13 B-52As and 17 detachable reconnaissance pods on 14 February 1951.^[44] The last major design change, also at the insistence of General LeMay, was a switch from the B-47 style tandem seating to a more conventional side-by-side cockpit which increased the effectiveness of the copilot and reduced crew fatigue.^[45] Both XB-52 prototypes featured the original tandem seating arrangement with a framed bubble-type canopy.^[46]

Pre-production

The YB-52, the second XB-52 modified with more operational equipment, first flew on 15 April 1952 with "Tex" Johnston as pilot.^[47][48] During ground testing on 29 November 1951, the XB-52's pneumatic system failed during a full-pressure test; the resulting explosion severely damaged the trailing edge of the wing, necessitating considerable repairs. A two-hour, 21-minute proving flight from Boeing Field, King County, in Seattle, Washington to Larson AFB was undertaken with Boeing test pilot Johnston and Air Force Lieutenant Colonel Guy M. Townsend.^[49] The XB-52 followed on 2 October 1952.^[50] The thorough development,^{[N 2]} including 670 days in the wind tunnel and 130 days of aerodynamic and aeroelastic testing, paid off with smooth flight testing. Encouraged, the Air Force increased its order to 282 B-52s.^[52]

Overview

The B-52 shared many technological similarities with the preceding Boeing B-47 Stratojet strategic bomber. The two aircraft utilized the same basic design, such as swept wings and podded jet engines,^[72] and the cabin included the crew ejection systems.^[73] On the B-52D, the pilots and ECM operator ejected upwards, while the lower deck crew ejected downwards; until the B-52G, the gunner had to jettison the tail gun and bail out.^[74] The B-52's official name Stratofortress has been used rarely in informal circumstances; it has become common among personnel to refer to the aircraft as the BUFF (Big Ugly Fat Fucker).^{[75][N 3]}

B-52H (61-0023), configured at the time as a testbed to investigate structural failures, still flying after its vertical stabilizer sheared off in severe turbulence on 10 January 1964. The aircraft landed safely^[77]

Structural fatigue was accelerated by at least a factor of eight in a low-altitude flight profile over that of high-altitude flying, requiring costly repairs to extend service life. In the early 1960s, the three-phase High Stress program was launched to counter structural fatigue, enrolling aircraft at 2,000 flying hours.^[78][79] Follow-up programs were conducted, such as a 2,000-hour service life extension to select airframes in 1966–1968, and the extensive Pacer Plank reskinning, completed in 1977.^[70][80] The wet wing introduced on G and H models was even more susceptible to fatigue, experiencing 60% more stress during flight than the old wing. The wings were modified by 1964 under ECP 1050.^[81] This was followed by a fuselage skin and longeron replacement (ECP 1185) in 1966, and the B-52 Stability Augmentation and Flight Control program (ECP 1195) in 1967.^[81] Fuel leaks due to deteriorating Marman clamps continued to plague all variants of the B-52. To this end, the aircraft were subjected to Blue Band (1957), Hard Shell (1958), and finally QuickClip (1958) programs. The latter fitted safety straps which prevented catastrophic loss of fuel in case of clamp failure.^[82]
In September 2006, the B-52 became one of the first US military aircraft to fly using alternative fuel. It took off from Edwards Air Force Base with a 50/50 blend of Fischer-Tropsch process (FT) synthetic fuel and conventional JP-8 jet fuel which was burned in two of the eight engines.^[83] On 15 December 2006, a B-52 took off from Edwards with the synthetic fuel powering all eight engines, the first time an Air Force aircraft was entirely powered by the blend. The seven-hour flight was considered a success.^[83] This program is part of the Department of Defense Assured Fuel Initiative, which aims to reduce crude oil usage and obtain half of its aviation fuel from alternative sources by 2016.^[83] On 8 August 2007, Air Force Secretary Michael Wynne certified the B-52H as fully approved to use the FT blend.^[84]

Avionics

A view of the lower deck of the B-52, dubbed the battle station

Ongoing problems with avionics systems were addressed in the Jolly Well program, completed in 1964, which improved components of the AN/ASQ-38 bombing navigational computer and the terrain computer. The MADREC (Malfunction Detection and Recording) upgrade fitted to most aircraft by 1965 could detect failures in avionics and weapons computer systems, and was essential in monitoring the Hound Dog missiles. The electronic countermeasures capability of the B-52 was expanded with Rivet Rambler (1971) and Rivet Ace (1973).^[85]
To improve safe day and night operations at low altitude, the AN/ASQ-151 Electro-Optical Viewing System (EVS), which consisted of a Low Light Level Television (LLLTV) and a Forward looking infrared (FLIR) system mounted in blisters under the noses of B-52Gs and Hs between 1972 and 1976.^[86] The navigational capabilities of the B-52 were later augmented with the addition of GPS in the 1980s.^[87] The IBM AP-101, also used on the Rockwell B-1 Lancer bomber and the Space Shuttle, was the B-52's main computer.^[88]
In 2007 the LITENING targeting pod was fitted, which increases the combat effectiveness of the aircraft during day, night and poor weather conditions in the attack of ground targets with a variety of standoff weapons, using laser guidance, a high resolution forward-looking infrared sensor (FLIR), and a CCD camera used to obtain target imagery.^[89] LITENING pods have been fitted to a wide variety of other US aircraft, such as the McDonnell Douglas F/A-18 Hornet, the General Dynamics F-16 Fighting Falcon and the McDonnell Douglas AV-8B Harrier II.^[90]

Armaments

The ability to carry up to 20 AGM-69 SRAM nuclear missiles was added to G and H models, starting in 1971.^[91] To further improve the B-52's offensive ability, Air Launched Cruise Missiles (ALCMs) were fitted.^[92] After testing of both the Air Force-backed Boeing AGM-86 and the Navy-backed General Dynamics AGM-109 Tomahawk, the AGM-86B was selected for operation by the B-52 (and ultimately by the B-1 Lancer).^[93] A total of 194 B-52Gs and Hs were modified to carry AGM-86s, carrying 12 missiles on underwing pylons, with 82 B-52Hs further modified to carry another eight missiles on a rotary launcher fitted in the aircraft's bomb-bay. To conform with the requirements of the SALT II Treaty for cruise missile capable aircraft to be readily identified by reconnaissance satellites, the cruise missile armed B-52Gs were modified with a distinctive wing root fairing. As all B-52Hs were assumed to be modified, no visual modification of these aircraft was required.^[94] In 1990, the stealthy AGM-129 ACM cruise missile entered service; although intended to replace the AGM-86, a high cost and the Cold War's end led to only 450 being produced; unlike the AGM-86, no conventional (non-nuclear) version was built.^[95] The B-52 was to have been modified to utilize Northrop Grumman's AGM-137 TSSAM weapon; however, the missile was canceled due to development costs.^[96]

A B-52D with antiflash white on the under side.

Those B-52Gs not converted as cruise missile carriers were subject to a series of modifications to improve their conventional bombing capability, being fitted with a new Integrated Conventional Stores Management System (ICSMS) and new underwing pylons which were able to be fitted with larger bombs or other stores than could be carried on the external pylons. Thirty B-52s were further modified to carry up to 12 AGM-84 Harpoon anti-ship missiles each, while 12 B-52Gs were fitted to carry the AGM-142 Have Nap stand-off air-to-ground missile.^[97] When the B-52G was retired in 1994, an urgent scheme was launched to restore an interim Harpoon and Have Nap capability,^{[N 4]} the four aircraft being modified to carry Harpoon and four to carry Have Nap under the Rapid Eight program.^[100]
The Conventional Enhancement Modification (CEM) program gave the B-52H a more comprehensive conventional weapons capability, adding the modified underwing weapon pylons used by conventional-armed B-52Gs, Harpoon and Have Nap, and the capability to carry new-generation weapons including the Joint Direct Attack Munition and Wind Corrected Munitions Dispenser guided bombs, the AGM-154 glide bomb and the AGM-158 JASSM missile. The CEM program also introduced new radios, integrated Global Positioning System into the aircraft's navigation system and replaced the under-nose FLIR with a more modern unit. Forty-seven B-52Hs were modified under the CEM program by 1996, with 19 more by the end of 1999.^[101][102]

Engines

USAF B-52 Stratofortress Engines

This section requires expansion with: describe original engine(s) used. (February 2013)

For a study for the U.S. Air Force in the mid-1970s, Boeing investigated replacing the engines, changing to a new wing, and other improvements to upgrade B-52G/H aircraft as an alternative to the B-1A, then in development.^[103] Boeing later suggested re-engining the B-52H fleet with the Rolls-Royce RB211 535E-4.^[104] This would involve replacing the eight Pratt & Whitney TF33s (total thrust 8 × 17,000 lb) with four RB211s (total thrust 4 × 37,400 lb); which would increase range and reduce fuel consumption, at a cost of approximately US$2.56 billion for the whole fleet (71 aircraft at $36 million each). A Government Accountability Office study concluded that Boeing's estimated savings of US$4.7 billion would not be realized and that it would cost US$1.3 billion over keeping the existing engines; citing significant up-front procurement and re-tooling expenditure, and the RB211's higher maintenance cost. The GAO report was subsequently disputed in a Defense Sciences Board report in 2003; the Air Force was urged to re-engine the aircraft without delay.^[105] Further, the DSB report stated the program would have significant savings, reduce greenhouse gas emissions, and increase aircraft range and endurance; in line with the conclusions of a separate Congress-funded study conducted in 2003.^[106] The re-engining has not been approved as of 2010.

Costs

	X/YB-52	B-52A	B-52B	B-52C	B-52D	B-52E	B-52F	B-52G	B-52H
Unit R&D cost	100 million (1955) 857 million (current)
Airframe		26.433 M (1955)	11.328 M (1955)	5.359 M (1955)	4.654 M (1955)	3.700 M (1955)	3.772 M (1955)	5.352 M (1955)	6.076 M (1955)
Engines		2.848 M (1955)	2.547 M (1955)	1.513 M (1955)	1.291 M (1955)	1.257 M (1955)	1.787 M (1955)	1.428 M (1955)	1.640 M (1955)
Electronics		50,761 (1955)	61,198 (1955)	71,397 (1955)	68,613 (1955)	54,933 (1955)	60,111 (1955)	66,374 (1955)	61,020 (1955)
Armament and ordnance		57,067 (1955) 489,075 (current)	494 K (1955) 4.23 M (current)	304 K (1955) 2.61 M (current)	566 K (1955) 4.853 M (current)	936 K (1955) 8.02 M (current)	866 K (1955) 7.42 M (current)	847 K (1955) 7.26 M (current)	1.508 M (1955) 12.9 M (current)
Flyaway cost		28.38 M (1955) 243.2 M (current)	14.43 M (1955) 123.7 M (current)	7.24 M (1955) 62 M (current)	6.58 M (1955) 56.4 M (current)	5.94 M (1955) 50.9 M (current)	6.48 M (1955) 56.4 M (current)	7.69 M (1955) 65.9 M (current)	9.29 M (1955) 79.6 M (current)
Maintenance cost per flying hour						925 (1955) 7,927 (current)	1,025 (1955) 8,784 (current)	1,025 (1955) 8,784 (current)	1,182 (1955) 10,130 (current)

Note: The original costs were in approximate 1955 United States dollars.^[107] Figures in tables noted with current have been adjusted for inflation.

Operational history

Introduction

Although the B-52A was the first production variant, these aircraft were used only in testing. The first operational version was the B-52B that had been developed in parallel with the prototypes since 1951. First flying in December 1954, B-52B, AF Serial Number 52-8711, entered operational service with 93rd Heavy Bombardment Wing (93rd BW) at Castle Air Force Base, California, on 29 June 1955. The wing became operational on 12 March 1956. The training for B-52 crews consisted of five weeks of ground school and four weeks of flying, accumulating 35 to 50 hours in the air. The new B-52Bs replaced operational B-36s on a one-to-one basis.^[108]
Early operations were problematic;^[109] in addition to supply problems, technical issues also struck.^[110] Ramps and taxiways deteriorated under the aircraft's weight, the fuel system was prone to leaks and icing,^[111] and bombing and fire control computers were unreliable.^[110] The two-story cockpit presented a unique climate control problem – the pilots' cockpit was heated by sunlight while the observer and the navigator on the bottom deck sat on the ice-cold floor. Thus, comfortable temperature setting for the pilots caused the other crew members to freeze, while comfortable temperature for the bottom crew caused the pilots to overheat.^[112] The J57 engines were proved to be unreliable; alternator failure caused the first fatal B-52 crash in February 1956,^[113] as a result the fleet was briefly grounded. In July, fuel and hydraulic issues grounded the B-52s again. In response to maintenance issues, the Air Force set up "Sky Speed" teams of 50 contractors at each B-52 base to perform maintenance and routine checkups, taking an average of one week per aircraft.^[114]

Three B-52Bs of the 93rd Bomb Wing prepare to depart March AFB for Castle AFB, California, after their record-setting round-the-world flight in 1957.

On 21 May 1956, a B-52B (52-0013) dropped a Mk-15 nuclear bomb over the Bikini Atoll in a test code-named Cherokee. It was the first air dropped thermonuclear weapon.^[115] From 24 to 25 November 1956, four B-52Bs of the 93rd BW and four B-52Cs of the 42nd BW flew nonstop around the perimeter of North America in Operation Quick Kick, which covered 15,530 miles (13,500 nmi, 25,000 km) in 31 hours, 30 minutes. SAC noted the flight time could have been reduced by 5 to 6 hours if the four inflight refuelings were done by fast jet-powered tanker aircraft rather than propeller-driven Boeing KC-97 Stratotankers.^[116] In a demonstration of the B-52's global reach, from 16 to 18 January 1957, three B-52Bs made a non-stop flight around the world during Operation Power Flite, during which 24,325 miles (21,145 nmi, 39,165 km) was covered in 45 hours 19 minutes (536.8 smph) with several in-flight refuelings by KC-97s.^{[117][N 5]}
The B-52 set many records over the next few years. On 26 September 1958, a B-52D set a world speed record of 560.705 miles per hour (487 kn, 902 km/h) over a 10,000 kilometers (5,400 nmi, 6,210 mi) closed circuit without a payload. The same day, another B-52D established a world speed record of 597.675 miles per hour (519 kn, 962 km/h) over a 5,000 kilometer (2,700 nmi, 3,105 mi) closed circuit without a payload.^[80] On 14 December 1960, a B-52G set a world distance record by flying unrefueled for 10,078.84 miles (8,762 nmi, 16,227 km); the flight lasted 19 hours 44 minutes (510.75 mph).^[118] From 10 to 11 January 1962, a B-52H set a world distance record by flying unrefueled, surpassing the prior B-52 record set two years earlier, from Kadena Air Base, Okinawa, Japan, to Torrejon Air Base, Spain, which covered 12,532.28 miles (10,895 nmi, 20,177 km).^[59] The flight passed over Seattle, Fort Worth and the Azores.

Air-to-air victories

During the Vietnam War, B-52D tail gunners were credited with shooting down two MiG-21 "Fishbeds". On 18 December 1972, tail gunner SSgt Samuel O. Turner's B-52 had just completed a bomb run for Operation Linebacker II and was turning away when a North Vietnamese Air Force MiG-21 approached.^[176] The MiG and the B-52 locked onto one another. When the fighter drew within range, Turner fired his quad (four guns on one mounting) .50 caliber machine guns.^[177] The MiG exploded aft of the bomber,^[176] a victory confirmed by MSG Lewis E. Le Blance, the tail gunner in a nearby Stratofortress. Turner received a Silver Star for his actions.^[178] His B-52, tail number 55-0676, is preserved on display with air-to-air kill markings at Fairchild AFB in Spokane, Washington.^[176]
On 24 December 1972, during the same bombing campaign, the B-52 Diamond Lil was headed to bomb the Thái Nguyên railroad yards when tail gunner A1C Albert E. Moore spotted a fast-approaching MiG-21.^[179] Moore opened fire with his quad fifties at 4,000 yd (3,700 m), and kept shooting until the fighter disappeared from his scope. TSG Clarence W. Chute, a tail gunner aboard another Stratofortress, watched the MiG catch fire and fall away. The Diamond Lil is preserved on display at the United States Air Force Academy in Colorado.^[179] Moore was the last recorded bomber gunner to shoot down an enemy aircraft with machine guns in aerial combat.^[177]
Vietnamese sources have attributed a third air-to-air victory to a B-52, a MiG-21 shot down on 16 April 1972.^[180] These victories make the B-52 the largest aircraft to be credited with air-to-air kills.^{[N 6]} The last Arc Light mission without fighter escort took place on 15 August 1973, as U.S. military action in Vietnam was wound down.^[181]

Post Vietnam service

B-52Bs reached the end of their structural service life by the mid-1960s and all were retired by June 1966, followed by the last of the B-52Cs on 29 September 1971; except for NASA's B-52B "008" which was eventually retired in 2004 at Edwards AFB, California.^[182] Another of the remaining B Models, "005" is on display at the Wings Over the Rockies Air and Space Museum in Denver, Colorado.^[183]

B-52H modified to carry two D-21 drones

A few time-expired E models were retired in 1967 and 1968, but the bulk (82) were retired between May 1969 and March 1970. Most F models were also retired between 1967 and 1973, but 23 survived as trainers until late 1978. The fleet of D models served much longer; 80 D models were extensively overhauled under the Pacer Plank program during the mid-1970s.^[184] Skinning on the lower wing and fuselage was replaced, and various structural components were renewed. The fleet of D models stayed largely intact until late 1978, when 37 not already upgraded Ds were retired.^[185] The remainder were retired between 1982 and 1983.^[186]
The remaining G and H models were used for nuclear standby ("alert") duty as part of the United States' nuclear triad. This triad was the combination of nuclear-armed land-based missiles, submarine-based missiles and manned bombers. The B-1, intended to supplant the B-52, replaced only the older models and the supersonic FB-111.^[187] In 1991, B-52s ceased continuous 24-hour SAC alert duty.^[188]
After the fall of the Soviet Union, all B-52Gs in service were destroyed per the terms of the Strategic Arms Reduction Treaty (START). The Aerospace Maintenance and Regeneraton Center (AMRC) cut the 365 B-52 bombers into pieces using a 13,000 lb guillotine. Completion of this task was verified by Russia via satellite and first-person inspection at the AMARC facility.^[189]

Gulf War and later

See also: Gulf War

Retired B-52s are stored at the 309th AMARG (formerly AMARC), a desert storage facility often called the "Boneyard" at Davis-Monthan AFB near Tucson, Arizona.^[190]

B-52 strikes were an important part of Operation Desert Storm. Starting on 16 January 1991, a flight of B-52Gs flew from Barksdale AFB, Louisiana, refueled in the air en route, struck targets in Iraq, and returned home – a journey of 35 hours and 14,000 miles round trip. It set a record for longest-distance combat mission, breaking the record previously held by an RAF Vulcan bomber in 1982.^[191][192] B-52Gs operating from bases at Jeddah, Saudi Arabia; RAF Fairford in the United Kingdom; Moron AB, Spain; and the island of Diego Garcia flew bombing missions over Iraq, initially at low altitude. After the first three nights, the B-52s moved to high-altitude missions instead, which reduced their effectiveness and psychological impact compared to the low altitude role initially played.^[193]
The conventional strikes were carried out by three bombers, which dropped up to 153 750-pound bombs over an area of 1.5 by 1 mi (2.4 by 1.6 km). The bombings demoralized the defending Iraqi troops, many of whom surrendered in the wake of the strikes.^[194] In 1999, the science and technology magazine Popular Mechanics described the B-52's role in the conflict: "The Buff's value was made clear during the Gulf War and Desert Fox. The B-52 turned out the lights in Baghdad."^[195] During Operation Desert Storm, B-52s flew about 1,620 sorties, and delivered 40% of the weapons dropped by coalition forces.^[1] There was one non-combat aircraft loss, and several aircraft received minor damage from enemy action.^{[citation needed]}
During the conflict, several claims of Iraqi air-to-air successes were made, including an Iraqi pilot, Khudai Hijab, who allegedly fired a Vympel R-27R missile from his MIG-29 and damaged a B-52G on the opening night of the Gulf War.^[196] However, the U.S. Air Force disputes this claim, stating the bomber was actually hit by friendly fire, an AGM-88 High-speed, Anti-Radiation Missile (HARM) that homed on the fire-control radar of the B-52's tail gun; the jet was subsequently renamed "In HARM's Way".^[197] Shortly following this incident, General George Lee Butler announced that the gunner position on B-52 crews was to be eliminated, and the gun turrets permanently deactivated, commencing on 1 October 1991.^[198]
From 2 to 3 September 1996, two B-52H bombers conducted a mission as part of Operation Desert Strike. The B-52s struck Baghdad power stations and communications facilities with 13 AGM-86C conventional air-launched cruise missiles (CALCM) during a 34-hour, 16,000-mile round trip mission from Andersen AFB, Guam – the longest distance ever flown for a combat mission.^[199]

A B-52H Stratofortress of the 2d Bomb Wing takes off from Andersen Air Force Base, Guam

Since the mid-1990s, the B-52H has been the only variant remaining in military service;^{[N 7]} it is currently stationed at:

• Minot AFB, ND – 5th Bomb Wing
• Barksdale AFB, LA – 2nd Bomb Wing (active Air Force) & 307th Bomb Wing (Air Force Reserve Command)
• One B-52H is assigned to Edwards AFB and is used by Air Force Material Command at the Air Force Flight Test Center.
• An additional B-52H is controlled by NASA as part of the Heavy-lift Airborne Launch program.^[200]

On 24 March 1999, when Operation Allied Force began, B-52 bombers bombarded Serb targets throughout the Federal Republic of Yugoslavia, including during the Battle of Kosare.^[201]
The B-52 contributed to Operation Enduring Freedom in 2001 (Afghanistan/Southwest Asia), providing the ability to loiter high above the battlefield and provide Close Air Support (CAS) through the use of precision guided munitions, a mission which previously would have been restricted to fighter and ground attack aircraft.^[202] B-52s also played a role in Operation Iraqi Freedom, which commenced on 20 March 2003 (Iraq/Southwest Asia). On the night of 21 March 2003, B-52Hs launched at least one hundred AGM-86C CALCMs at targets within Iraq.^[203]
In August 2007, a B-52H ferrying AGM-129 ACM cruise missiles from Minot Air Force Base to Barksdale Air Force Base for dismantling was mistakenly loaded with six missiles from which the nuclear warhead was not removed. The weapons did not leave USAF custody and were secured at Barksdale.^[204][205]
As of April 2011, 94 of the original 744 B-52 aircraft were operational in the U.S. Air Force (85 Air Force and 9 Air Force Reserve. Four of 18 B-52Hs from Barksdale AFB that are currently being retired are in the "boneyard" of 309th AMARG at Davis-Monthan AFB as of 8 September 2008

Variants

Production numbers^[2]

Variant	Produced	Entered Service
XB-52	2 (1 redesignated YB-52)	prototypes
B-52A	3
NB-52A	1 Modified B-52A
B-52B	50	29 June 1955
RB-52B	27 Modified B-52Bs
NB-52B	1 Modified B-52B
B-52C	35	June 1956
B-52D	170	December 1956
B-52E	100	December 1957
B-52F	89	June 1958
B-52G	193	13 February 1959
B-52H	102	9 May 1961
Grand total	744 production

The B-52 went through several design changes and variants over its 10 years of production.^[107]

XB-52

Two prototype aircraft with limited operational equipment, used for aerodynamic and handling tests

YB-52

One XB-52 modified with some operational equipment and re-designated

B-52A

Only three of the first production version, the B-52A, were built, all loaned to Boeing for flight testing.^[47] The first production B-52A differed from prototypes in having a redesigned forward fuselage. The bubble canopy and tandem seating was replaced by a side-by-side arrangement and a 21 in (53 cm) nose extension accommodated more avionics and a new sixth crew member.^{[N 9]} In the rear fuselage, a tail turret with four 0.50 inch (12.7 mm) machine guns with a fire-control system, and a water injection system to augment engine power with a 360 US gallon (1,363 L) water tank were added. The aircraft also carried a 1,000 US gallon (3,785 L) external fuel tank under each wing. The tanks damped wing flutter and also kept wingtips close to the ground for ease of maintenance.^[218]

NB-52A carrying an X-15

NB-52A

The last B-52A (serial 52-0003) was modified and redesignated NB-52A in 1959 to carry the North American X-15. A pylon was fitted under the right wing between the fuselage and the inboard engines with a 6 feet x 8 feet (1.8 m x 2.4 m) section removed from the right wing flap to fit the X-15 tail. Liquid oxygen and hydrogen peroxide tanks were installed in the bomb bays to fuel the X-15 before launch. Its first flight with the X-15 was on 19 March 1959, with the first launch on 8 June 1959. The NB-52A, named "The High and Mighty One" carried the X-15 on 93 of the program's 199 flights.^[219]

NASA's NB-52B Balls 8 (lower) and its replacement B-52H on the flight line at Edwards Air Force Base

B-52B/RB-52B

The B-52B was the first version to enter service with the USAF on 29 June 1955 with the 93rd Bombardment Wing at Castle AFB in California.^[218] This version included minor changes to engines and avionics, enabling an extra 12,000 pounds of thrust to be produced using water injection.^[220] Temporary grounding of the aircraft after a crash in February 1956 and again the following July caused training delays, and at mid-year there were still no combat-ready B-52 crews.^[113]

Of the 50 B-52Bs built, 27 were capable of carrying a reconnaissance pod as RB-52Bs (the crew was increased to eight in these aircraft).^[47] The 300 pound (136 kg) pod contained radio receivers, a combination of K-36, K-38, and T-11 cameras, and two operators on downward-firing ejection seats. The pod required only four hours to install.^[113]

Seven B-52Bs were brought to B-52C standard under Project Sunflower.^[221]

NB-52B

The NB-52B was B-52B number 52-0008 converted to an X-15 launch platform. It subsequently flew as the "Balls 8" in support of NASA research until 17 December 2004, making it the oldest flying B-52B. It was replaced by a modified B-52H.^[222]

B-52C

The B-52C's fuel capacity (and range) was increased to 41,700 US gallons by adding larger 3000 US gallon underwing fuel tanks. The gross weight was increased by 30,000 pounds (13,605 kg) to 450,000 pounds. A new fire control system, the MD-9, was introduced on this model.^[138] The belly of the aircraft was painted with antiflash white paint, which was intended to reflect thermal radiation away after a nuclear detonation.^[223]

RB-52C

The RB-52C was the designation initially given to B-52Cs fitted for reconnaissance duties in a similar manner to RB-52Bs. As all 35 B-52Cs could be fitted with the reconnaissance pod, the RB-52C designation was little used and was quickly abandoned.^[223]

B-52D dropping 500-lb bombs

B-52D

The B-52D was a dedicated long-range bomber without a reconnaissance option. The Big Belly modifications allowed the B-52D to carry heavy loads of conventional bombs for carpet bombing over Vietnam,^[220] while the Rivet Rambler modification added the Phase V ECM systems, which was better than the systems used on most later B-52s. Because of these upgrades and its long range capabilities, the D model was used more extensively in Vietnam than any other model.^[138] Aircraft assigned to Vietnam were painted in a camouflage colour scheme with black bellies to defeat searchlights.^[66]

B-52E

The B-52E received an updated avionics and bombing navigational system, which was eventually debugged and included on following models.^[220]

One E aircraft (AF Serial No. 56-0631) was modified as a testbed for various B-52 systems. Redesignated NB-52E, the aircraft was fitted with canards and a Load Alleviation and Mode Stabilization system (LAMS) which reduced airframe fatigue from wind gusts during low level flight. In one test, the aircraft flew 10 knots (11.5 mph, 18.5 km/h) faster than the never exceed speed without damage because the canards eliminated 30% of vertical and 50% of horizontal vibrations caused by wind gusts.^[224]

B-52F

This aircraft was given J57-P-43W engines with a larger capacity water injection system to provide greater thrust than previous models.^[220] This model had problems with fuel leaks which were eventually solved by several service modifications: Blue Band, Hard Shell, and QuickClip.^[82]

B-52G on static display at Langley Air Force Base in Hampton, Virginia

B-52G

The B-52G was proposed to extend the B-52's service life during delays in the B-58 Hustler program. At first, a radical redesign was envisioned with a completely new wing and Pratt & Whitney J75 engines. This was rejected to avoid slowdowns in production, although a large number of changes were implemented.^[220] The most significant of these was the brand-new "wet" wing with integral fuel tanks which considerably increased the fuel capacity; gross aircraft weight went up by 38,000 pounds (17,235 kg) compared with prior variants. In addition, a pair of 700 US gallon (2,650 L) external fuel tanks was fitted under the wings.^[225] In this model, the traditional ailerons were eliminated. Instead, spoilers provided roll control. The tail fin was shortened by 8 feet (2.4 m), water injection system capacity was increased to 1,200 US gallons (4,540 L), and the nose radome was enlarged.^[226] The tail gunner manning the 4 .50 caliber machine guns (quad mounted in a remote controlled tail turret on the G-model (ASG-15), the guns were later removed from all operational aircraft) was relocated to the main cockpit and was provided with an ejection seat.^[225] Dubbed the "Battle Station" concept, the offensive crew (pilot and copilot on the upper deck and the two bombing navigation system operators on the lower deck) faced forward, while the defensive crew (tail gunner and ECM operator) on the upper deck faced aft.^[138] The B-52G entered service on 13 February 1959 (a day earlier, the last B-36 was retired, making SAC an all-jet bomber force). 193 B-52Gs were produced, making this the most produced B-52 variant. Nearly all B-52Gs were destroyed in compliance with the Strategic Arms Reduction Treaty of 1992; a few examples remain in museums and as static displays.^[227]

B-52H

The B-52H had the same crew and structural changes as the B-52G. The most significant upgrade was the switch to TF33-P-3 turbofan engines which, despite the initial reliability problems (corrected by 1964 under the Hot Fan program), offered considerably better performance and fuel economy than the J57 turbojets.^[138][226] The ECM and avionics were updated, a new fire control system was fitted, and the rear defensive armament was changed from machine guns to a 20 mm M61 Vulcan cannon (later removed in 1991–94).^[225] A provision was made for four GAM-87 Skybolt ballistic missiles. The aircraft's first flight occurred on 10 July 1960, and it entered service on 9 May 1961. This is the only variant still operational. A total of 744 B-52s were built. The last production aircraft, B-52H AF Serial No. 61-0040, left the factory on 26 October 1962.^[228]

XR-16A

Allocated to the reconnaissance variant of the B-52B but not used and the aircraft were designated RB-52B instead

General characteristics

• Crew: 5 (pilot, copilot, radar navigator (bombardier), navigator, and Electronic Warfare Officer)
• Length: 159 ft 4 in (48.5 m)
• Wingspan: 185 ft 0 in (56.4 m)
• Height: 40 ft 8 in (12.4 m)
• Wing area: 4,000 sq ft (370 m²)
• Airfoil: NACA 63A219.3 mod root, NACA 65A209.5 tip
• Empty weight: 185,000 lb (83,250 kg)
• Loaded weight: 265,000 lb (120,000 kg)
• Max. takeoff weight: 488,000 lb (220,000 kg)
• Powerplant: 8 × Pratt & Whitney TF33-P-3/103 turbofans, 17,000 lbf (76 kN) each
• Fuel capacity: 47,975 U.S. gal (39,948 imp gal; 181,610 L)
• Zero-lift drag coefficient: 0.0119 (estimated)
• Drag area: 47.60 sq ft (4.42 m²)
• Aspect ratio: 8.56

Performance

• Maximum speed: 560 kt (650 mph, 1,047 km/h)
• Cruise speed: 442 kt (525 mph, 844 km/h)
• Combat radius: 4,480 mi (3,890 nmi, 7,210 km)
• Ferry range: 10,145 mi (8,764 nmi, 16,232 km)
• Service ceiling: 50,000 ft (15,000 m)
• Rate of climb: 6,270 ft/min (31.85 m/s)
• Wing loading: 120 lb/ft² (586 kg/m²)
• Thrust/weight: 0.31
• Lift-to-drag ratio: 21.5 (estimated)

Armament

• Guns: 1× 20 mm (0.787 in) M61 Vulcan cannon originally mounted in a remote controlled tail turret on the H-model, removed from all current operational aircraft in 1991
• Bombs: Approximately 70,000 lb (31,500 kg) mixed ordnance; bombs, mines, missiles, in various configurations

Avionics

• Electro-optical viewing system that uses platinum silicide forward-looking infrared and high resolution low-light-level television sensors
• LITENING Advanced Targeting System^[256]
• Sniper Advanced Targeting Pod^[257]
• IBM AP-101 computer^[88]

• ^{From Wikipedia}