Development of the B-52 had begun in June 1945 after the AAF had directed Air Materiel Command (AMC) to consider second generation intercontinental bombers eventually to replace the B-36 Peacemaker in post-war service. On 23 November a series of specifications were issued, calling for a bomber with an operating radius of 5,000 miles and a speed of 300 mph at 34,000 ft. The crew was to be five, plus gunners for an undetermined number of 20 mm cannon turrets. A 10,000 lb bomb load was specified, as well as provision for a six-man relief crew. On 13 February 1946 the new requirement was circulated among the aviation giants and Boeing, Glenn L. Martin Company and Consolidated Vultee Aircraft Corporation subsequently submitted cost quotations and preliminary design data. Boeing’s proposal was the Model 462, which looked very like a larger version of the wartime B-29 Superfortress. It was a conventional monoplane design with a shoulder-mounted straight wing of 221 ft (67.4 m) span and an area of 3,250 sq ft (269 sq m). The circular-section fuselage was 161 ft 2 in (49.1 m) long. Power was to be provided by six Wright XT35 Typhoon turboprops, each producing 5,500 shaft hp and driving six-bladed propellers. Turboprop engines rather than pure jets were favoured because of heavy fuel consumption, which would make it difficult if not impossible to meet the range requirement. The four main wheels of the nosewheel undercarriage each retracted separately into the four inner engine nacelles. The gross weight was 360,000 lb.
Even with the turboprops the Model 462 failed to meet the range requirement but on 5 June 1946 Boeing was awarded an engineering study and preliminary design contract and in mid-June the Boeing design was designated XB-52. On 28 June Boeing were directed to build a full-scale mock-up, begin preliminary design engineering, and supply test data. In October 1946 the United States Army Air Force had misgivings about the XB-52 and it was decided that the Boeing design was just too large and expensive. Its performance too was questioned. It was an improvement over the B-36 but air force chiefs concluded that the Model 462 offered little in the way of growth potential. Major General Earle E. Partridge, assistant Chief of Air Staff for operations, told Boeing that it did not meet the range requirement. Boeing responded with a smaller and lighter version weighing just 230,000 lb, known as the Model 464, which was powered by Wright XT-35 turboprops. Major General Laurence C. Craigie, chief of the USAAF Engineering Division, recommended that this design be adopted.
In November 1946 Lieutenant General Curtis E. LeMay, the then Deputy Chief of Air Staff for Research and Development, disagreed. In the Second World War LeMay’s drive and dynamism was such that both in Europe and the Pacific he almost single-handedly changed the concept of long-range bombing forever. LeMay wanted a B-52 with a higher cruising speed and longer range. In December the USAAF requested that a study be carried out for a four-engined bomber with a range of 12,000 miles, a cruising speed of 400 mph, and the ability to carry atomic weapons. In response Boeing offered Models 464-16 and 464-17, both of which were still powered by four Wright XT-35 turboprops but with significantly higher power output and improved overall performance. These two proposals were much larger and heavier than the earlier Model 464 and the gross weight was now estimated at 400,000 lb, wingspan, 205 ft (62.4 m), wing area 3,000 sq ft (248.7 sq m) and length 156 ft (47.5 m). The increase in range would be achieved partly by the adoption of large external fuel tanks under the outer wings. The top speed was estimated at 440 mph at 35,000 ft. The 464-16 was a ‘specialized’ version intended to deliver nuclear weapons and would carry only a 10,000 lb bombload over long distances, while the 464-17 was optimized for conventional warfare and was capable of carrying a bombload as high as 90,000 lb over a much shorter range.
There was no military budget to fund both projects simultaneously so the USAAF opted for the Model 464-17 which, apart from range limitations, seemed to meet most requirements. It was argued that with mid-air refuelling now available, range limitations could be overcome. Lieutenant General LeMay however, was still not satisfied. He felt that the Model 464-17 was still too large and costly and he could foresee a future procurement of only 100 aircraft. By this time General Craigie was against the project altogether, claiming that the XB-52 offered little improvement over the B-36 and that it would probably be rendered obsolete before it could enter service. As a result, the Model 464-17 was to be shelved. LeMay, however suggested that a six-month grace period ensue before the final decision was made.
During the first few months of 1947 Boeing reworked the design again and again, until they arrived at the Model 464-29, which was powered by the same four XT-35 turboprops as previous versions, but now featured a sharply tapered wing with 20 degrees of sweepback. An extended dorsal fin was provided. The wingspan remained at 205 ft and the weight at 400,000 lb. A major change was the adoption of a centre-line landing gear underneath the fuselage similar to that fitted to the B-47 but with forward and aft units much closer together, plus a set of outrigger wheels which retracted into the outer engine nacelles. The estimated maximum speed was 445 mph. As it turned out, however, this performance was not enough to save the Model 464-29. On 11 December 1947 Air Materiel Command was directed to cancel the Boeing contract but a protest from William M. Allen, chairman of Boeing, persuaded Secretary of the Air Force, Stuart Symington, to put off a decision.
Late in 1947 the air force was still looking for more effective means of delivering nuclear weapons and a Heavy Bombardment Committee was set up to explore ways of doing so. The committee declared that speed and altitude were the most crucial requirements if an aircraft was to be capable of delivering an atomic weapon in heavily defended airspace. On 8 December a new set of requirements was issued officially, which called for a special-purpose bomber with an 8,000 mile range and a 500–550 mph cruising speed. All of this was clearly impossible using turbofans. In January 1948 Symington informed Boeing that its existing proposal was unsuitable, although no final decision would be made until other possibilities such as the Northrop YB-49 flying wing had been explored. Boeing engineers meanwhile had repeatedly attempted to improve the performance of the XB-52 design and in January 1948 produced in the Model 464-35. The four Wright XT35 engines now drove a set of coaxial propellers, the wingspan was reduced to 185 ft (56.4 m), the wing area to 2,600 sq ft (215.5 sq m) and the length to 131 ft 4 in (40 m). Considerable attention had been paid to weight reduction, and gross weight was now down to 280,000 lb. The maximum speed was estimated at 500 mph at 41,000 ft, and the maximum range was 11,635 miles.
This performance was still not ideal but was closer to the Air Force requirement and in April Boeing presented a complete Phase II proposal for the design, development and testing of two XB-52s based on the Model 464-35. The USAF, which had always ruled out jet engines to power their long-range bombers because of their high fuel consumption, asked Boeing in May to explore the possibility of using them to power the B-52. This could have delayed the project still further, but, there was greater sense of urgency in political and military circles when in late June Berlin was blockaded by Soviet forces and the Cold War became hot. Boeing’s Phase II proposal was rubber-stamped that July when that company’s Model 464-40 was finalized. This was essentially identical to the Model 464-35 but was powered by eight Westinghouse XJ40-13-12 turbojets in underwing podded pairs. The gross weight was 280,000 lb; the wingspan was 185 ft (56.4 m) and the length 130 ft 9 in (41.4 m). The performance was slightly better, especially at high altitude, and the maximum speed was now 507 mph at 47,000 ft.
The Air Force Project Officer favoured the new proposal but concerns about the increased fuel consumption moved the government to direct Boeing to use the turboprop-powered Model 464-35 as the basis of its two XB-52s. General Howard A. Craig, Deputy Chief of Staff for Materiel felt that the jet engine had still not progressed sufficiently to replace turboprop power. Boeing was urged not to abandon turbojet studies, however, even though there seemed no immediate requirement to produce a jet-powered long-range bomber.
Lieutenant General Curtis E. LeMay, who transferred from the US Air Forces in Europe (USAFE) to assume command of SAC on 19 October 1948 came out strongly in favour of the B-52 project. Never one for half measures, during his nine-year tenure (1948–57) SAC became the world’s most powerful military force, operating on a global basis. On arrival at SAC HQ he had demanded to see the war plan. There was no war plan, he was informed. Within weeks of taking over, he had replaced SAC’s deputy commander, chief of staff, director of operations and director of plans and replaced them with generals who were all veterans of the Pacific strategic bombing campaign. As he said in his memoirs, ‘My determination was to put everyone in SAC into this frame of mind: We are at war now. So that, if actually we did go to war the very next morning or even that night, we would stumble through no period in which preliminary motions would be wasted. We had to be ready to go then…’ In March 1949 LeMay proposed that SAC’s capabilities be increased to the point where it was possible to deliver 133 atomic bombs against seventy major Soviet cities in a single, all-out strike. This plan was accepted in December 1949. When he left on 30 June 1957 to become Air Force Vice-Chief of Staff, his legacy to SAC was a strategic air force that had become the only American nuclear deterrent to prevent a pre-emptive Communist strike on the USA. And it was the B-52 that formed the backbone of the manned bomber strategic deterrent. However, the B-52 might never have reached production had it not been for this far-sighted individual.
When, on 21 October 1948, a Boeing team led by Edward C. Wells, Vice-President Engineering, arrived at Wright Field to confer with Colonel Henry E. ‘Pete’ Warden and other officials of the Wright Air Development Center about the turboprop-powered B-52, their carefully prepared design drawings and data were rendered redundant. Warden, who had been responsible for encouraging Major General Kenneth B. Wolfe, the AMC commander, of the need for the B-47, told the Boeing engineering team that the turboprop design was dead in the water and that the turbojet was to be adopted! In 1947 aircraft engine manufacturers Pratt & Whitney had received a contract for the development of the 10,000 hp PT4 (T45) turboprop as a possible powerplant for the B-52 if the Wright T35 engine was not successful. The PT4 had a dual axial flow compressor of thirteen stages and could easily be converted to a pure turbojet should the need arise. Presented with a fait accompli, the Boeing design team carefully considered the new scenario and the next morning Colonel Warden was informed that a new design proposal would be ready by the following Monday. Holed up in the Van Cleeve Hotel in Dayton all that weekend the team prepared a drastically reshaped design called the Model 464-49, which housed eight J57 engines in the podded arrangement first identified in the Model 464-40 proposal. The wingspan was unchanged at 185 ft (56.4 m) but the angle of sweep was increased a further 15 degrees to 35; and the wing area was increased by 1,400 sq ft to 4,000 sq ft (331.6 m). Performance estimates were worked out with the help of Boeing engineers at the other end of the phone lines in Seattle. The maximum speed was estimated to be 565 mph at 46,500 ft and combat radius with a 10,000 lb bombload was estimated at 3,550 miles. The gross weight was estimated at 330,000 lb. George S. Schairer, Boeing’s chief aerodynamicist, converted this new design into model form by using balsa wood purchased from a local hobby shop in downtown Dayton.
On the Monday morning the team delivered its new proposal to the air force. Because jet engines eliminated the potential problems associated with propeller-driven systems it was thought that a jet powered B-52 could probably be built almost in the same timeframe as the turboprop variant then under development. Warden liked the new proposal and recommended that the B-52 be developed as pure jet-powered aircraft. At once Boeing stopped all work on the Model 464-35 mock-up, which was almost finished, while Pratt & Whitney were instructed to proceed with the J57 engine. In January 1949, following a final evaluation, the Board of Senior Officers gave the specification their approval and on the 26th Boeing was informed that work on the jet-powered B-52 would proceed under the original contract. From 26 to 29 April 1949 the swept-wing turbojet-powered XB-52 mock-up was inspected against a backdrop of political and military infighting. Severe budgetary limitations were still being imposed by the Truman administration on the Defense Department. Some air force chiefs – General Orville R. Cook, Director of Procurement and Industrial Planning at AMC, in particular – retained doubts about range, since the J57 engine at this time had an estimated combat radius of only 2,700 nautical miles. Cook favoured a review of the entire programme and was even prepared to schedule another competition. LeMay had no such doubts. He suggested that the answer to the range problem lay in engine development and that it was unnecessary to accept inferior performance in either speed or range.
Early on in the B-52 development LeMay insisted that it had to be able to carry a large conventional as well as nuclear payload and tasked his Director of Plans, Major General John P. McConnell, with ensuring that this was carried out. LeMay continued to involve himself in every aspect of B-52 technical development and when he visited Seattle to see the prototypes he was displeased to see Boeing’s proposed tandem pilot seating reminiscent of the B-47. He was instrumental in getting it changed to a side-by-side seating arrangement. This would enhance crew coordination and provide a single set of engine instruments and engine controls visible to both pilots. In the process this change permitted an electromagnetic countermeasures officer (ECM), later renamed the electronic warfare officer (EWO), to be added to the crew whereas initially the B-52 was to have only a pair of pre-set AN/APT-5 jammers installed. In August 1951 the air force adopted the side-by-side arrangement but the two prototypes retained the tandem seating arrangement. The normal crew was five, with pilot and co-pilot seated in tandem under a bubble-type canopy in the forward nose. The navigator and radar operator sat side by side on a lower deck, while the gunner sat in a separate cockpit in the extreme tail. In an inflight emergency, the pilot, co-pilot and EWO ejected upward and the navigator and radar operator ejected downward. The tail gunner did not have an ejection seat. He jettisoned the turret by firing four explosive bolts and would then have to bale out. All production machines would have side-by-side seating for the pilot and co-pilot. Entry to the cockpit was via a door located on the fuselage underside offset to starboard and hinged at the rear. The gunner in the tail had his own entry door in the starboard aft fuselage side below the horizontal tail surface. The gunner was normally isolated from the rest of the crew but he could move forward via a crawl-way to the weapons bay and from there he had access to the main crew compartment via a small access door that was cut into the aft cabin pressure bulkhead. However, cabin depressurization was necessary before he could do this.
By November 1949, convinced that the insufficient range of the Model 464-49 could seriously jeopardise the outcome of the B-52 project, Boeing made a big effort to improve it, an issue which resulted in the Model 464-67. The wing span remained the same but the length of the fuselage was increased to 152 ft 8 in (46.5 m) to allow more space for fuel. As a result the Model 464-67 was a much heavier version with a gross weight now estimated at 390,000 lb and a combat radius estimated at 3,500 miles. LeMay and his staff officers at SAC viewed it favourably, which boded well for B-52 development.
When on 26 January 1950 a conference at USAF HQ reconsidered the future of the B-52, it attracted a raft of proposals from Douglas, Republic, Fairchild and Convair (who proposed the prototype YB-60 an eight-jet swept-wing version of the B-36), as well as a turboprop aircraft and two new designs based on the B-47. (In June 1951 the first of 399 Boeing B-47B Stratojet swept-wing six engined strategic medium jet bombers had entered SAC service. More than 1,600 B-47E/RB-47E models followed from early 1953.) In addition several missile aircraft were put forward as cost-effective alternatives. No firm decision was reached, however, and General LeMay retained his conviction that the B-52 was still the optimum solution for the strategic mission.
When In February the Air Staff requested performance and cost data for all the proposals, LeMay asked the Board of Senior Officers to accept the Boeing Model 464-67 in place of the Model 464-49. On 24 March they approved his choice, although Boeing must have been concerned that a definite commitment to production was still not forthcoming. It was not until early 1951 that a decision finally to put the B-52 into production was reached. By then the Korean War was in progress and US-Soviet relations were at an all-time low. LeMay was determined to modernize his strategic bombing force with the B-52 and on 9 January 1951 USAF Chief of Staff General Hoyt S. Vandenberg approved a proposal that the B-52 be acquired as a replacement for the B-36. On 14 February 1951 a contract for an initial batch of thirteen B-52As for delivery beginning April 1953 was signed. (Only three B-52As were built, at a cost of $29.3 million each; the rest were completed as B-52Bs, by which time the cost of the aircraft had dropped to $14.4 million each). SAC wanted a dual-role aircraft, which could be fitted with reconnaissance sensors housed in a capsule that was easily removable so that the aircraft could quickly be reconfigured from bomber to reconnaissance while the Air Staff wanted the B-52 for a purely reconnaissance role.
By late 1951 the two B-52 prototypes were ready for roll-out. Both had been ordered originally as XB-52s but the second aircraft was redesignated as YB-52 after the 1949 proposal had recommended installing some operational equipment so that it could serve as a production prototype. In the event however, there was very little difference between the two aircraft. Eight Pratt & Whitney YJ57-P-3 axial-flow turbojets delivering 8,700 lb static thrust powered both the XB-52 (49-230) and YB-52 (49-231). Each of these aircraft had a shoulder-mounted wing with a sweepback angle of 35 degrees. The wingspan was 185 ft (56.4 m) with an area of 4,000 sq ft (331.6 m). The rather thin wing, similar in design to the B-47, was set at an angle of incidence of 6 degrees, deemed necessary because of the tandem undercarriage layout, which did not permit the aircraft to rotate on take-off. The wing structure on the centre line of the fuselage had a thickness ratio of 16.2 per cent, declining gradually to only 8 per cent at the tip. Nevertheless the wings contained bladder-type cells for fuel. The thin wings had a considerable amount of flexibility and the feature was at first disconcerting to the pilots when they saw the wings during considerable turbulence slowly flapping to an incredible deflection of 32 ft at the tip. When sitting on the ground with no fuel load, the wings sat high enough so that the outrigger wheels did not actually touch the ground. However, when fully loaded with fuel, the wheels always touched the ground, only rising off the runway after sufficient lifting force has been generated during take-off. When airborne, the wings generally had an upward curvature. The eight J57 turbojets were carried two each in four underwing pods suspended under the wings on pylons. The engines were situated beneath and ahead of the forward edge of the wing. Careful positioning of the engine pods helped to limit the drag rise at high speed and also served to alleviate load factors. The pylons also doubled as wing fences and helped to delay the onset of the stall.
The wings were fitted with four segments of Fowler-type flaps, two on the trailing edge of each wing. The total flap area was 797 sq ft (80.4 sq m). Only two settings were available, fully up or fully down, with the down angle being 35 degrees. Aerodynamic surfaces on the B-52 wing consisted of a combination of ailerons and spoilers. The ailerons were located on the mid-wing trailing edges between the inner and outer flap sections, while the seven-segment spoilers were located somewhat further out on the upper wing surface. When operated asymmetrically, the ailerons provided adequate roll control during most normal flight operations, but an additional measure of control could be obtained by using the spoilers during landing or in-flight refuelling. When deployed symmetrically, the wing spoilers could act as airbrakes, making a deceleration chute, like that used on the B-47, during final approach unnecessary. However, a 44 ft brake chute, stowed in a hatch underneath the rear fuselage, was still needed to reduce the landing roll.
The vertical fin was 48 ft 3 in (14.7 m) tall and it incorporated a nearly full-span rudder of rather narrow chord. The entire vertical fin assembly could be folded sideways to allow the aircraft to be wheeled into standard hangars. (Later, on the B-52G a major redesign saw the vertical tail reduced in height by 92 in (2.3 m) to lessen aerodynamic load on the rear fuselage in low-level flight.) The horizontal tail surfaces had a span of 52 ft (15.8 m) and an area of 900 sq ft (74.6 m). The horizontal tail was of the fully variable type, pivoting through an arc of 13 degrees (9 up, 4 down). Much of the space in the fuselage was occupied by fuel tanks, the upper sections located just behind the cockpit to just aft of the rear main undercarriage members being used almost exclusively for fuel. The weapons bay occupied almost the entire section of the lower fuselage between the forward and rear undercarriage members. It was 28 ft (8.5 m) long and 6 ft (1.8 m) wide and was enclosed by double-panel doors. Three interconnected and hydraulically actuated lower panels on each side made up the section of the bomb bay doors that could be opened in flight. While on the ground, the hinged upper panels could be swung back to provide additional clearance for loading and unloading of weapons.
The landing gear used double twin-wheeled units mounted side by side underneath the fuselage, one forward and one to the rear. To prevent the wingtips from dragging on the ground during take-off or landing, there were small outrigger wheels, which retracted into the outer wing. However, the main wheels gave the aircraft enough ground stability so that it could stand by itself without the need for the outrigger wheels. The main landing gear retraction process was fairly complicated, with the wheels swivelling through almost 90 degrees before folding to lie flat within the storage bays. The retraction was asymmetric, with the port units folding forward and the starboard ones folding aft. Any one of the four main units could be lowered independently. A unique feature of the landing gear was the ability of the main units to rotate up to 20 degrees left or right of the line of flight. This facilitated crosswind landings and take-offs by permitting the aircraft to point directly into the wind while the wheels remained aligned with the runway.
An unusual feature of the B-52 was the use of a pneumatic system as the primary power source in the operation of all auxiliary functions aboard the aircraft. High-pressure, hightemperature air was bled from the second-stage compressor of each jet engine, and carried by ducts to the desired locality in the aircraft, where it was transformed into electrical or hydraulic energy by air-turbine-driven power packs. There were ten turbine-driven hydraulic pumps, which supplied pressure at 3,000 psi to drive the brakes, steering mechanism, spoilers, bomb bay doors, and the adjustable stabilizer. The pneumatic system also drove air turbine alternators, which provided the electrical power for the aircraft.
At Seattle on 29 November 1951 the XB-52 prototype, 49-230, was rolled out of the assembly hall and into the flight test-hangar. It was subjected to a series of ground tests and checkouts during which the pneumatic system failed during a full-pressure test and the resulting blow-out severely damaged the wing trailing edge and this required that the aircraft be moved back into the production hall for repair. Boeing and the air force kept news of this secret and attributed the delay to the installation of further equipment. Almost a year later than originally planned, the XB-52 took off on its maiden flight on 2 October 1952. It remained airborne for more than two hours.
In the meanwhile, the YB-52 prototype, 49-231, which was to have waited until changes resulting from testing of the XB-52 were incorporated, became the first B-52 to fly. It was rolled out on 15 March 1952. The first flight on 15 April 1952 went from Boeing Field in Seattle to Moses Lake AFB (later renamed Larson AFB), Washington. Boeing’s chief test pilot A. M. ‘Tex’ Johnston and Lieutenant Colonel Guy M. Townsend of the USAF Air Research and Development Command were at the controls. The fuel capacity, at 38,865 US gallons, was greater than in any previous production aircraft, giving a maximum take-off weight of 405,000 lb. Flying chase was USAF flight test photo pilot Captain Harley Beard in a Lockheed F-80 Shooting Star. Beard was flying to the right of the YB-52 when he announced that he was going to take a picture of the Stratofortress. Townsend radioed back with his Mississippi drawl: ‘Y’ all know ya can’t take a picture of a Boein’ airplane without the mountain in the background.’ Beard therefore performed a half roll around the port side and proceeded to photograph the B-52 with Mount Rainier in the background! The YB-52 remained airborne for two hours fifteen minutes and was almost entirely successful, with only a few minor problems being encountered. One of the main landing gears failed to retract properly (photographs released to the press had the landing gear units censored out), and there were defects in the liquid oxygen system and a leaking engine oil valve. By the beginning of October 1952 the YB-52 had logged fifty hours in the air and had begun Phase I flight trials.
Phase II tests between 3 November 1952 and 15 March 1953 revealed some problems with engine reliability. The J57s were prone to surge when normal throttle movements were undertaken at high altitude with low engine inlet temperatures, and there was a tendency to pitch up and roll to starboard when approaching the stall. Also the braking system was unable to bring the Stratofortress to a halt within the required distance. After an extensive series of flight tests beginning in 1957 both the XB-52 and the YB-52 were used by the Wright Air Development Center at Wright Patterson AFB Ohio. The XB-52 flew as a six-engined aircraft with four J57s inboard and two J75s outboard. After logging 783 flying hours the YB-52 was donated to the USAF Museum at Wright Patterson AFB in Ohio on 27 January 1958. (Both aircraft were scrapped in the mid-1960s.)
Between June 1946 and April 1952 Boeing had expended in excess of three million engineering hours on the B-52. More than three years of flight-testing went into the XB-52, YB-52, three B-52As and ten B-52Bs before the aircraft were ready for delivery to SAC. A total of nine and half years elapsed between the basic requirement being established by the air force and the first operational aircraft being delivered. The balance of the 744 B-52s produced would be delivered during the following 7 years. It was all a far cry from the summer of 1953 when the air force agreed plans for a total procurement of just 282 B-52s, enough to equip seven bomb wings in SAC, each with an establishment of about thirty aircraft.
On 12 January 1954 John Foster Dulles, the Secretary of State, declared that, ‘Local defences must he reinforced by the further deterrent of massive retaliatory power and that the defence of the West depended primarily upon a capacity to retaliate instantly by means and at places of our own choosing’.
No B-52As entered service with the air force. Deliveries of the first operational version, the B-52B, to the 93rd Bombardment Wing, did not begin until 29 June 1955 when the first (52-8711) was accepted and was flown by the Commanding Officer, Brigadier General William E. Eubank Jr, to Castle AFB, California. Over the next few months his B-47s, which had been operated by the wing for barely a year, were traded in for B-52Bs and on 8 January 1955 the 4017th Combat Crew Training Squadron was activated. The 4017th performed all B-52 crew training for the 93rd and for two additional B-52 wings, the 42nd at Loring AFB, Maine with B-36s and the 99th at Westover AFB, Massachusetts with B-47s. However, when the training mission became too great a task for just one squadron, the 93rd Wing’s other three squadrons took over the flight-training role and in 1956 the 4017th assumed responsibility for ground instruction. In September 1955 SAC planned for 576 B-52s equipping eleven wings each with forty-five aircraft in three squadrons. The 93rd Bomb Wing was only declared combat ready on 12 March 1956 with thirty B-52Bs (out of a final complement of forty-five B-52s – fifteen per squadron). The last of the B-52Bs was delivered in August; B-52Ds began reaching SAC in June 1956 and the final five B-52Cs reached the air force in December.
In 1956 America was at last able to ‘retaliate instantly by means and at places of her own choosing’. During Operation Redwing Cherokee on 21 May B-52B 52-0013 of the Air Research and Development Command dropped a Mk 15 hydrogen bomb capable of producing a yield of 3.75 megatons at the Bikini Atoll in the Pacific. The 10 ft long weapon, weighing 7,600 lb, fell 3 miles short of the target due to an error in timing, but measuring equipment aboard JB-52B The Tender Trap confirmed that while delivery accuracy needed perfecting the B-52 was a primary delivery system for weapons of mass destruction. Now any act of aggression by the Communist bloc could result in strategic nuclear strikes on Soviet or Chinese targets. SAC further demonstrated strategic bombing capability in spectacular fashion on 24 and 25 November 1956. Four B-52Bs of the 93rd Bombardment Wing and four B-52Cs of the 42nd Bombardment Wing made a non-stop flight around the perimeter of North America in Operation Quick Kick. Most noted of this mission was Lieutenant Colonel Marcus L. Hill Jr, whose flight in 53-0388 (with four refuellings by KC-97 Stratotankers) originated at Castle AFB and landed at Baltimore, Maryland, covering 12,271 miles in thirty-one hours thirty minutes.
By December 1956 SAC had upped the procurement requirement to a total of 603 B-52s. In 1957 the first B-52Ds went to the 42nd Bomb Wing at Loring AFB, Maine, where they replaced B-52Cs. All 170 production models were delivered by November 1957 and they equipped five wings in SAC, which had three more wings awaiting delivery of 100 B-52Es. These first entered service with SAC in December 1957 but production problems with the B-52F delayed its entry until June 1958. By the close of 1957 five B-52 wings with three squadrons each had been activated and another three were in the process of reequipping. In 1958 the number of B-52 wings SAC required was increased to fourteen with forty-two squadrons. By 1 June 1958 SAC included four numbered air forces (Second, Eighth, Fifteenth and Sixteenth) and three direct-reporting air divisions under the command of General Thomas S. Power, who had taken over from General LeMay on 1 July 1957. The command had over 258,000 personnel, 22 B-36 Peacemakers, 1,367 B-47 Stratojets, 380 B-52s and 962 KC-97 and KC-135A aerial refuelling tankers. It had been anticipated that a more advanced bomber would replace the Stratojet by 1957; but however events dictated that it would have to continue in service until well into the 1960s but this only after a massive life extension modification programme. The last B-47 was not retired until 1966.