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NAA's original proposal for WS-110A. The "floating panels" are large fuel tanks containing conventional JP-4 fuel used during the long subsonic cruise, each is the size of a B-47. Once ejected, the engines would burn "HEF", or zip fuel, during the high-speed dash phase.

WS-110A ("Weapon System 110A") was a project by the United States Air Force in the 1950s to develop a supersonic bomber aircraft capable of delivering nuclear weapons. Proposals for such an aircraft were submitted by Boeing and North American Aviation. Although the program was put on indefinite hold before any actual designs were completed, it paved the way for the B-70 program.


Boeing Aircraft Corporation's MX-2145 Project with Rand Corporation that started in January 1954 explored what sort of aircraft would be needed to deliver the various nuclear weapons then under development. Providing for a long range and high payload were obvious requirements, but they also concluded that after bomb-release the plane would need supersonic speed to escape the weapon's critical blast-radius. Jet engines of the time had poor fuel efficiency.[citation needed] An aircraft capable of carrying a reasonable bomb load to the Soviet Union from the continental United States had to carry a large fuel load (and thus be very large itself) due to the unrefueled range required.[1][2]

The aviation industry had been examining this problem for some time. There was considerable interest in the use of nuclear-powered aircraft in the bomber role from the mid-1940s.[3][N 1] Nuclear engines in aircraft used the heat generated by a nuclear reactor in place of jet fuel, giving it virtually unlimited cruising range.[4] In addition to solving the range issue, these aircraft could be flown to holding areas away from the airbases and kept in the air for extended periods of time, making them immune to sneak attack. Accordingly, Boeing developed plans for a nuclear-powered bomber equipped with afterburners that used chemical fuel. Lockheed and Convair proposed similar designs.[citation needed]

Another possibility was the use of boron-enriched "zip fuels", which improved the energy density of the fuel by about 40%.[5] Various U.S. government agencies had been experimenting with zip fuels for some time, and they believed that once the problems were solved, zip fuel would become almost universal for high-speed aircraft. Although the advantages of a zip-fueled aircraft would not be as great as those of a nuclear-powered one, it would offer a real performance increase and was a relatively straightforward development of existing engines and fuels.[5]

Air Force studies

In October 1954, the Air Force issued General Operational Requirement No. 38, which was quite general and called simply for an intercontinental manned bomber which would replace the B-52 beginning in 1965. March 1955's GOR.81 was more specific, calling for a nuclear-powered bomber with a combat radius of 11,000 nautical miles (20,000 km), capable of flying up to 1,000 miles (1,600 km) at a speed greater than Mach 2 at altitudes greater than 60,000 feet (18,000 m) with a 20,000 lb (9,100 kg) payload, revising this to 25,000 lb (11,000 kg) in GOR.82 later that month.[6][7]

The Air Research and Development Command (ARDC) decided to separate the two approaches, and issued a requirement for "Weapon System 110A", which asked for a Mach 0.9 cruising speed and "maximum possible" speed during a 1,000-mile (1,600 km) entrance and exit from the target. The target date for the first operational wing of these bombers was July 1964, reduced a year in comparison to earlier GOR's. The nuclear approach became "Weapon System 125A", while the ICBM work was organized under "Weapon System 107A".[8]

In early 1955, the Air Force issued GOR.96, which called for an intercontinental reconnaissance system with the same general requirements as WS-110A, called WS-110L.[9] The two requirements were combined soon afterwards, becoming Weapon System 110A/L. The nuclear-powered version was dropped during this period, given the problems in that program's development, as well as a general feeling of optimism about the zip fuels. In June 1955 the Air Staff directed that the details of WS-110A/L be released to the aviation industry and that a request for proposals be issued. Although six contractors were given the requirements, only Boeing and North American Aviation (NAA) submitted proposals. On 8 November 1955, the Air Force issued letter contracts to both Boeing and North American for Phase 1 development. The contracts called for models, design reports, wind tunnel tests, plus a mock-up.[9]

In 1956, initial designs were presented by the two companies. Although zip fuels improved range, the overall effect was not very large, perhaps 10%, so both designs featured huge wingtip fuel tanks that could be jettisoned before a supersonic run on the target. In the case of the North American design, the entire outer portion of the wings was jettisoned as well, resulting in an aircraft that looked somewhat like a very large F-104 Starfighter after being "broken up".

The Air Force evaluated their designs and in September 1956 deemed them too large and complicated; the huge fuel load resulted in takeoff weights of 700,000 pounds, making safe operation from existing runways extremely difficult. They were also far too large to fit in existing hangars. Curtis LeMay was not enthusiastic about the design, claiming "Hell, this isn't an airplane, it's a three-ship formation."[8] NAA and Boeing's study contracts were extended to further develop their bomber designs.[7] The next month the program was put "on hold", although the companies were told to continue any low-level development they could.


  1. Quote by Theodore von Kármán (1945): "The size and performance of the craft driven by atomic power would depend mainly on ... reducing the engine weight to the limiting value which makes flight at a certain speed possible."[3]
  1. York 1978, p. 70.
  2. "B-70 Valkyrie". Retrieved 24 May 2011. 
  3. 3.0 3.1 von Kármán, Theodore. "Where We Stand: First Report to General of the Army H. H. Arnold on Long Range Research Problems of the Air Forces with a Review of German Plans and Developments". Atomic Energy for Jet Propulsion. Washington, D.C.: Government Printing Office, 22 August 1945.
  4. Bikowicz, Brian D.. "Atomic Powered Aircraft – Politics". Retrieved 24 May 2011. 
  5. 5.0 5.1 Schubert, Dave. "From Missiles to Medicine: The development of boron hydrides". Pioneer Magazine. March 2001.
  6. North American XB-70A Valkyrie, J Baugher.
  7. 7.0 7.1 Jenkins 1999, Ch. 1
  8. 8.0 8.1 Lost Classics – North American XB-70 Valkyrie
  9. 9.0 9.1 Pace 1986, p. 14.
  • Jenkins, Dennis R.; Landis, Tony R. (2004). Valkyrie : North American's Mach 3 Superbomber. North Branch: Specialty Press Publishers and Wholesalers. ISBN 1-58007-072-8. 
  • Jenkins, Dennis R. (1999). B-1 Lancer :The Most Complicated Warplane Ever Developed. New York: McGraw-Hill. ISBN 0-07-134694-5. 
  • Pace, Steve. "Triplesonic Twosome." Wings, Volume 18, No. 1, February 1988.
  • York, Herbert Jr. Race to Oblivion: A Participant's View of the Arms Race. New York: Simon & Schuster, 1978. ISBN 0-06-181898-4.

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