Air University Review, March-April 1967

The Extra-Super Blockbuster

Dr. William S. Coker

On 5 March 1948 a U.S. Air Force B-29 Superfortress dropped the world’s largest conventional bomb on the test range at Muroc AFB, California. This 22-ton missile was nearly twice as heavy as the largest bomb previously dropped, which weighed a mere 12½ tons.1 The bomb, oldest of aircraft weapons, had come a long way since 1 November 1911, when Lieutenant Gavotti of the Italian Army threw the first one from an aircraft. Although the weight of Gavotti’s bomb is unknown, it was described as “a little larger than an orange.”2 The bomb dropped from the Superfortress in 1948 weighed almost 44,000 pounds. It was 26 feet 10 inches long and 4 feet 6 inches in diameter. The largest bomb dropped during World War II, the British Grand Slam, weighed a little over 22,000 pounds.3

The size and weight of bombs have always been limited by the capability of aircraft to carry them. In January 1945, with the prospect of getting the B-36 into production before the war ended, the Army Air Forces requested the Ordnance Department to develop a bomb not larger than 60 inches in diameter nor longer than 322 inches. The B-36 was expected to be able to carry a 72,000-lb payload 4600 miles, or an even heavier load over shorter distances.4 After some preliminary work Ordnance advised that a bomb meeting those specifications and weighing about 42,000 pounds could be built. Within a few months an order for 100 of the bombs was placed with the A.O. Smith Corporation of Milwaukee. The end of the war brought a cutback in the order, but this company eventually manufactured 57 of the giants, which were to be used for flight-testing and the development of bomb-handling equipment. 5

These bombs never enjoyed a nickname or fancy title such as those given the British earthquake bombs, Tall Boy and Grand Slam. The Milwaukee Journal once referred to the 44,000-pounder as an “extra-super-blockbuster,” but the name never caught on. Thus, the largest bomb ever made was destined to go through life with the ordinary nomenclature “Bomb, General Purpose, 42,000-lb., T12.” One slight change did occur, however, when after three years the Ordnance Committee decided to redesignate it “Bomb, General Purpose, 44,000-lb., TI2.” In part, this was done because the bomb was overweight. Changes in fabrication had added a few pounds, and the finished product weighed in excess of 43,000 pounds. Later changes in tail fins and filler material even caused weight differences between individual bombs. The new nomenclature, it was asserted, was also to save confusion, since the bombs had been variously referred to as 42,000-lb, 43,000-lb, and 44,000-lb bombs.6

The idea for such mammoth bombs originated with Dr. B. N. Wallis of Vickers-Armstrongs (Aircraft) Ltd. Wallis, a noted aircraft designer, became interested in huge bombs early in the war. He had hit upon the idea of breaching Germany’s large gravity dams, and after early calculations and experiments Wallis concluded that it would require a bomb weighing 70,000 pounds to do the job. For obvious reasons a 35-ton missile was out of the question: The largest aircraft on British drafting boards could hardly have lifted a 10-ton bomb. Wallis was forced to revise his plans. The out-growth was the 9250-lb “dam-busting” weapon or “store.” This weapon arrived on target in an ingenious manner. Instead of being dropped on the target, this barrel-shaped bomb was released several hundred yards upstream and skipped over the water until it hit the upper structure of the dam, then its spinning motion caused it to sink to the right depth to destroy the dam. The Moehne and Eder dams in Germany were breached on the night of 16-17 May 1943 by use of this plan and weapon. The courage and daring of the RAF bomber crews of 617 Squadron who flew the mission were in no small part responsible for its great success.7

Wallis had also developed the principle of the so-called earthquake bomb, which was designed to bury itself in the ground close to its objective, the subsequent underground explosion creating an effect similar to an earthquake. The 12,000-lb Tall Boy was the first of the earthquake bombs produced. Its bomb blast was so great that it “caused entire buildings to disintegrate and collapse into rubble.”8 The Tall Boy was first used on the night of 8 June 1944 when 19 of them were dropped on the Saumur railway tunnel. One direct hit caused the roof of the tunnel to fall in. By the end of the war in Europe, 854 Tall Boys had been dropped on concrete submarine pens, E-boat bases, and V-weapon sites, as well as other targets in Germany and occupied countries.9

The success of the Tall Boy and the need for an even larger bomb led to the development of its big brother, the 22,000-lb Grand Slam. Great secrecy surrounded the manufacture of the Grand Slam, and the company that made the casing labeled it a “boiler.” This subterfuge apparently fooled no one, for in the pubs around Sheffield it was ingloriously called “the big bastard.” The first Grand Slam was test-dropped on the same night that two of them were scheduled for a combat mission. Two Lancasters had been modified to carry them, and while waiting for the weather to clear at their target, the Bielefeld Viaduct, the RAF crews received this terse message concerning the experimental drop of the bomb, “The beast went off all right!”l0 First used operationally at Bielefeld on 14 March 1945, 41 Grand Slams were dropped by the RAF before the war was over. 11

The Army Air Forces, which had never used the big earthquake bombs, by late 1944 began to see their possibilities. They could be employed as general-purpose bombs for blast and fragmentation effect, to create cave-ins and earth shock, and to get at important underground installations. In addition to the development of the T10 and T14, the U.S. equivalents of the Tall Boy and Grand Slam, the anticipated bomb-carrying capabilities of the B-36 led not unnaturally to the development of the colossal T12. Shortly after V-J Day, five of the T12s were turned over to the Air Force for testing.12

The B-36 was test-flown for the first time in August 1946. Even then the first models of the B-36 could not carry the big bomb, and it would be some months before they could be modified to handle it. The Air Force, which was interested in experimenting with the 44,000-lb bomb, decided that a modified B-29 could handle the job until a B-36 was available.

Toward the end of the war a B-29 had been converted to carry two 22,000-lb bombs, one under each wing, for use against Japan. The two atomic bombs, the Fat Man and Little Boy, made use of this special B-29 unnecessary.13

The aircraft chosen for the alterations was a B-29A, No. 44-62263. The Wichita, Kansas, Division of the Boeing Company performed the fuselage work. Part of the body section under the wings was cut away, the rear bomb-bay doors were removed entirely, and the front bomb-bay doors were cut away to allow the nose of the bomb to protrude. In spite of these modifications, about half the missile hung out beneath the plane. The aircraft also required special instrumentation to measure wing deflection, “G” forces exerted on the plane, and acceleration of the aircraft upon release of the bomb. A separate instrument panel with the necessary equipment was installed so that a special camera mounted near the panel could photograph the instruments. The wing tips were painted with black and yellow strips of known width which could be photographed and the wing deflection computed. The instrumentation work was accomplished at Muroc AFB.14

In addition to the modification of the B-29, a special bomb lift had to be built to handle the 44,000-lb missile. The Boeing Company designed a 50,000-lb lift that would hoist a 25-ton bomb 12½ feet in the air, roll it 360 degrees in either direction, shift it 4 inches either side of center and 10 inches fore or aft, and tilt it 6 degrees up or down. One man operating six levers could load one of the bombs into an aircraft. 15

Squadron C, 608th AAF Base Unit, Chemical & Ordnance Test Group, stationed at Muroc, was selected to drop the first TI2.16 Preparations for the drop continued throughout the fall of 1947 and early 1948. After modification, the Superfortress and its crew were sent to Eglin AFB, Florida, for special training. Air Force and Ordnance experts refused to speculate on what might happen to the B-29 when it suddenly became 22 tons lighter after the bomb was dropped.

The Superfort reached Muroc in December, and the 50,000-lb lift arrived the following month. A series of minor problems then delayed the actual drop for some time. The lift had been damaged en route to California and had to be repaired. Squadron C armament personnel had to be trained to operate it. A pit had to be dug to get the bomb and lift under the B-29. After money problems for digging the pit had been solved and the earth excavated, a heavy rainfall filled it with water and delayed pouring of the concrete. The same rain also saturated the Muroc Dry Lake from which the aircraft would have to take off, and it was feared that the program might be further delayed. Several days were devoted to loading the bomb into the plane and to static drop tests. It was also necessary to load the bomb into the Superfort, weigh it, and find the center of gravity before the first take-off could be made. A crew of weight and balance experts from the Sacramento Air Depot were called in to assist in that function. But in spite of these little difficulties, everything was ready for the big event by early March.17

Just before noon on 5 March 1948, the bomb was released from B-29 No. 2263, piloted by Captain William A. Looney. The Group historian recorded the event in these words, “On this date the heaviest bomb the world has ever known, weighing 43,755-lbs was dropped from a B-29 aircraft from an altitude of 25,000 feet. The entire mission was highly successful and the bombing results were excellent.”18 By 19 April 1948 the personnel of Squadron C and B-29 No. 2263 were veterans, having dropped six of the extra-super blockbusters.19 Their part in the operation was completed.

The use of a B-36 to drop the bomb after it had already been dropped by the much smaller B-29 would almost have been an anticlimax except for one thing: the B-36 dropped two of them on the same mission. On 29 January 1949 at Fort Worth, Texas, Consolidated Vultee B-,36 No. 43, piloted by Major Stephen P. Dillon, carried the greatest bomb load ever lifted to that date into the sky—over 43 tons. The weight lifted was equivalent to that of a B-17 Flying Fortress. Including bombs and fuel, the B-36 grossed over 300,000 pound—not startling in terms of today’s behemoths, but in 1949 it was a whopping amount. 20

The two bombs were flown by the B-36 from Fort Worth to the bombing range at Muroc AFB, where the first bomb was released at 35,000 feet. Then Dillon took the plane to 40,000 feet, where the second one was dropped. The B-36 made the round trip nonstop, a flight of about 2900 miles. The official announcement proclaimed it “a normal test flight.”21

All these T12 bombs dropped were unarmed. Eventually the bomb was exploded, but the details have not yet been released. The results of the first explosive-filled 22,000-lb Grand Slam dropped by the British produced a crater 30 feet deep and 124 feet in diameter. It is readily evident that the 44,000-lb Tl2 could produce a sizable earthquake.22

One advantage of the T12 over an atomic bomb is obvious: If the military situation called for heavy blasting of large areas through which our men would eventually have to advance, the 44,000-lb bomb could be used without having to worry about radiation contamination from an exploded A-bomb. The Air Force has also recognized its possibilities in creating cave-ins and earth shock and in getting at important underground installations. Dropping a string of the extra-super blockbusters in areas of known Viet Cong subterranean strongholds might just force them to give up such positions, bringing the enemy to the surface and into the open where more conventional and less expensive methods and weapons could do the trick.

Hattiesburg, Mississippi


1. AF press release, 10 March 1948. The press release called it a 21-ton bomb, but it weighed 43,755 pounds.

2. Constance McLaughlin Green, Harry C. Thomson, and Peter C. Roots, The Ordnance Department: Planning Munitions for War, a volume in the U.S. Army in World War II, The Technical Services series (Washington: Government Printing Office, 1955), p. 451.

3. AF press release, 10 March 1948; Paul Brickhill, The Dam Busters (London: Evans Bros., Ltd., 1951), p. 31.

4. Major J. A. Swaney, “Record of Army Ordnance Research and Development, Bomb Development,” p. 370; Wesley Frank Craven and James Lea Cate (eds.), The Army Air Forces in World War II (7 vols.; Chicago: University of Chicago Press, 1948-1958), VI, 245.

5. Swaney, “Bomb Development,” p. 370; R. J. Kastenholz, A. O. Smith Corp. to Chief of Ordnance, Attn: Col. C.H.M. Roberts, 8 June 1949, AF Historical Division, Archives, Maxwell AFB, Alabama.

6. Clipping from Milwaukee Journal, 12 October 1945; memorandum from Col. C. H. M. Roberts to the Secretary, Ordnance Technical Committee, 13 May 1949.

7. Brickhill, p. 31 et passim. In 1963 Dr. Wallis explained the details of the weapon and the strategy employed in its use in an unpublished article entitled “The ‘Dam Busting’ Weapon.” A copy of this study was provided the author by Vickers-Armstrongs (Aircraft) Ltd.

8. Green, et al., pp. 470-71.

9. Charles Webster and Noble Frankland, The Strategic Air Offensive Against Germany (4 vols.; London: Her Majesty’s Stationery Office, 1961), I, 183, II, 294, III, 181, 204n3.

10. Brickhill, pp. 249-52.

11. Webster and Frankland, III, 203-4.

12. Swaney, p. 370; Green, et al., pp. 454, 471.

13. The Fat Man, the plutonium-type atomic bomb, was exploded over Nagasaki. It was 128 inches long, 60 inches in diameter, and weighed 10,000 pounds. The Little Boy, the uranium-type atomic bomb, was released over Hiroshima. It was 120 inches long, 28 inches in diameter, and weighed 9000 pounds. Gene Gurney, The Man in the Air (New York: Crown Pub., Inc.; 1962), p. 330.

14. AF press release, 10 March 1948; Unit History, Squadron C, 608th AF Base Unit, Muroc AFB, California, semiannual summary, March 1948, file 240.07608, AF Archives.

15. AF press release, 10 March 1948; Boeing Plane Talk, No. 15, 5 August 1949.

16. History, Squadron C, July 1947.

17. History, Squadron C, December 1947, January-March 1948.

18. Historical Record, 608th AFBU, Phillips Field, Aberdeen Proving Ground, Maryland, 1 January-30 June 1948, p. 15.

19. The bombs were dropped on 5, 10, 12, 18, and 22 March and 19 April 1948. History, Squadron C, March and April 1948.

20. Washington Post, 30 January 1949.

21. Ibid.

22. Webster and Frankland, III, 203-4.


Illustrations accompanying this article are used with kind permission of the Imperial War Museum (London), Vickers-Armstrongs (Aircraft) Ltd, Boeing Company, General Dynamics, and the United States Air Force.


Dr. Williams S. Coker (Ph.D., University of Oklahoma) is Assistant Professor of History, University of Southern Mississippi. He retired as a senior master sergeant in 1962 after serving over 21 years in the Air Force. Until 1950 he flew as a crew member (radio operator-gunner) on B-17s, B-24s, B-29s, and C-97s. Subsequently he worked in the communications operations and education and training career fields. Dr. Coker was an instructor in the AFROTC program at the University of Oklahoma, 1955-58, and has since been a visiting assistant professor of history at Oklahoma and at Kansas State University. He has published articles in various historical and professional journals.


The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.

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