The XB-70A had its genesis in Boeing Aircraft Corporation's Project MX-2145, in which the contractor conducted studies relating to the type of weapon system required to deliver high-yield special weapons. The contractor, along with the Band Corporation, considered various types of weapon system carriers. Among them were manned intercontinental bombers, delivering both gravity bombs and pilotless parasite bombers; manned bombers, air-refueled by tankers to attend their ranges and cover round-trip intercontinental distances; manned aircraft and drone bomber combinations; and unmanned bombers. During these studies Air Force Headquarters requested enlargement of the study program to include possible trade-off information; for example, the potential results of trading weight for speed, weight for range, or speed for range.
Boeing presented the requested information on 22 January 1954, pointing out the possibilities of a bomber aircraft powered by chemically augmented nuclear powerplants. For the first time, it appeared feasible to develop a weapon system of a reasonable size possessing the unlimited range characteristics of nuclear propulsion,' plus a high-altitude, supersonic dash capability. The development of nuclear propulsion for aircraft or missiles originated in 1945. In May 1946, the Army Air Forces signed a "letter of intent" with the Fairchild Engine and Airplane Corporation, thereby conferring on the highly classified NEPA (Nuclear Energy for the Propulsion of Aircraft) program a legal right to exist. While favoring the program, General LeMay, then Deputy Chief of Air Staff for Research and Development, said the work to be performed under NEPA would be somewhat speculative. In March 1954, Boeing presented promising data on a chemically augmented, nuclear-powered aircraft. At the same time, both the Convair Corporation and Lockheed Aircraft Corporation, under contracts with the Office of Aircraft Nuclear Propulsion, submitted similar data.
In the fall of 1954, the Air Force Council endorsed 2 independent but simultaneous development programs, one for a nuclear bomber capable of short bursts of supersonic speed; the other, for a subsonic, chemically powered, conventional bomber. General Operational Requirement No. 81, issued in Match 1955, specifically called for the development of a nuclear-powered weapon system that would be capable of performing a strategic mission of 11,000 nautical miles in radius, of which 1,000 miles were to be traveled at speeds in excess of mach 2, at an altitude of more than 60,000 feet. The Air Force Council's announcement closely followed the October publication of General Operational Requirement No. 38. The document was brief. It simply called for an intercontinental bombardment weapon (a piloted bomber) that would replace the B-52 and stay in service during the decade beginning in 1965.
The Air Force, on 22 March 1955, put out a second general operational requirement, No. 82, which superseded No. 38. Like its predecessor, the new general operational requirement was short. It called for a piloted strategic intercontinental bombardment weapon system that would be capable of carrying a 20,000-pound load of high-yield nuclear weapons, a requirement increased to 25,000 pounds by a September amendment. But the task of defining the Air Force's new project fell to the Air Research and Development Command. The command, therefore, had issued a study requirement, designated No. 22, which identified the Air Force's future new bomber as "Weapon System 110A" and established 1963 as the target date for the first wing of 30 operational vehicles. Study Requirement 22's performance objectives were mach .9 for cruise speed and "maximum possible" speed during a 1,000-nautical mile penetration. Still, high speed was of less importance than the penetration altitude and radius. A revision of Study Requirement 22 on 15 April stipulated that the new weapon system's cruise speed should not be less than mach .9, unless a lower speed would result in a significant range increase. There were other important changes. Instead of the subsonic requirement covered by General Operational Requirement 38, maximum possible "supersonic" speed within the combat zone was desired. On I 1 October, Air Research and Development Command amended the revised Study Requirement 22. The amendment set July 1964 as the target date for the first operational wing of B-70s-so designated in February 1958. The purpose of the delay was to avoid financial and overall weapon system risks, if at all possible. In 1955, the Air Research and Development Command estimated the weapon system's costs through fiscal year 1962 at $2.5 billion. The estimate covered development, test aircraft, and 30 operational bombers, but assumed that a nuclear bomber would also be developed, that a new engine for the chemically powered bomber would be created, and that the price of certain subsystems, earmarked for the B-70, would be borne by the nuclear aircraft program.
In early 1955, the Air Force released another general operational requirement (No. 96) for an intercontinental reconnaissance system having similar objectives as the previously established bombardment system, known as Weapon System 110A. In July, the Air Research and Development Command issued a study requirement of General Operational Requirement 96 that validated a reconnaissance version of the B-70. The reconnaissance system was identified as Weapon System 110L. The 2 systems were combined soon afterward, becoming in the process Weapon System 110A/L.
In June 1955, the Air Staff directed that development of Weapon System 110A/L be initiated as soon as possible with a multiple, competitive "Phase I" program. The use of "phase" contracts was not new, having been approved as early as 1944 by the Army Air Forces to facilitate the termination of contracts dealing with highly experimental and, therefore, very uncertain programs. Although 6 eligible contractors were contacted, only the Boeing Airplane Company and North American Aviation, Incorporated chose to submit proposals.
On 8 November 1955, the Air Force awarded letter contracts to both Boeing and North American for the Phase I development of Weapon System 110A/L. Boeing's letter contract amounted to $2.6 million; that of North American, to $1.8 million. Each contractor had to furnish a design for the required weapon system; provide models, drawings, specifications, reports, and other data; conduct studies and wind tunnel tests, and construct a mockup. The mockup was to be completed and ready for Air Force inspection within 2 years of the date on which the contractor accepted the contract. Contractor fees could not exceed $450,000.
The 2 letter contracts became definitive in 1956. The Boeing contract, AF33(600)-31802, signed on IS March, specified a total estimated cost of $19.9 million; the North American contract, AF33(600)-31801, signed on 16 April, $9.9 million, subject to renegotiation. The Air Force, in its definitive contracts, allotted originally $4.5 million to Boeing and $1.8 million to North American.
Concurrent with the letter contracts of 1955, the Air Force established specific requirements that were included in the final documents signed in 1956. 'Ib begin with, each contract emphasized that the purpose of the entire program was to develop, test, and produce for wing strength by 1963 (much sooner than decided in October 1955) a chemically powered weapon system which, in conjunction with the nuclear-powered bomber, would replace the B/RB-52 as a "first line operational weapon."
With regard to operational characteristics, the new weapon system was to rely primarily on nuclear weapons to accomplish its mission, and the origin and termination of its operations were to be within the limits of the North American continent. The Air Force specified that weapon system I l0A/L would have to be capable of performing during the day, at night, and in any kind of weather. A minimum unrefueled radius of 4,000 nautical miles, and a desirable extended radius of 5,500 nautical miles were required, with aerial refueling allowed in the latter case. Finally, the minimum target altitude was to be 60,000 feet, and the contracts reiterated that cruise speed could not be less than mach .9, with maximum supersonic dash speed in the combat zone.
These were exacting characteristics. Studies of conventional aircraft had shown that no such performance could be obtained with proven design techniques. The Air Force acknowledged that the ability to satisfy its demands, particularly the radius-of-action and speed requirements, would depend on the use of high-energy fuels, new engines, new design techniques, and some other break-through in the state-of-the-art by the operational date of 1963. The Air Force also made sure that the contractors knew that while range and speed trade-offs would be acceptable in order to assure maximum supersonic dash at a "practical" gross weight, every reduction would have to be minimal. Finally, the new weapon system's configuration would have to allow for the easy addition of state-of-the-art improved subsystems and components, not initially incorporated.
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