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Aviation History
1946
1946 - 1046.PDF
538 FLIGHT MAY 30TH, A stately Boeirg B-29 Superfortress of "Project Ruby " over Hertfordshire. with 22,000-pounders. - "Flight " photogroith Three of these aircraft are bombing the Farge pens BOMBS VERSUS CONCRETE casing or filling is at fault but to provide data on the resistance of concrete to "hammer" blows. Technical details of the bombs are withheld, but the story of their development is illuminating. In 1941 the largest penetrating bomb available to the R.A.F. was the thousand-pounder. True, a small number of 2,000-lb armour-piercers existed, but although these had a very small charge / weight ratio they were designed primarily for use against ships. The thousand-pounder could not reach any great depth and dissipated a great deal of energy upwards in forming a crater. It was realized that if the same bomb could be made to penetrate deep enough to cause a spherical cavity in the earth, energy dissipation would be more in the form of a pressure wave, with "earthquake" characteristics, but the small weight of the bomb prevented this being achieved. During the same year Mr. Wallis, of Vickers-Armstrongs, Ltd., produced calculations for a bomb to use a pressure wave for its destructive value, rather than cratering and fragmentation. He calculated that the depth of penetration should be about 130ft in ordinary soil, and specified a ten-ton bomb to contain about six tons of explosive. Released from 40,000ft, he considered that this would produce the desired pressure effect, causing underground installations to collapse, though not directly hit. At that time, of course, no R.A.F. bomber was capable of carrying the load to the required height and for the necessary range, but the project was not forgotten. Two years later the Germans, harassed by thousand-pound bombs, began to burrow under- ground and to protect vital installations with thick concrete. Still the R.A.F. had no aircraft capable of carrying a ten-ton bomb to 40,000ft, though the goal was half reached. Thus a com- promise was indicated and took the form of the 12,000-pounder carried by the Lancaster. Credit for this development must go not only to Mr. Wallis but to Mi. Roy Chad wick, the English Steel Corporation of Sheffield and Air Chief Marshal Sir Wilfred Fiee- man, then Chief Executive of M.A.P. ; this was made clear by Group Captain Wynter-Morgan, likewise I The : ths low build of Superfortress ; necessitates the! use ; the : with of a pit for bombing - up a " GrandSlam." intimately concerned with the bomb's development, during a demonstration at Bovington of the modified B-29 and Lancaster. Early in 1944 the 12,000-pounder was in pro- duction and the first bomb was used by 617 Squadron against the Saumur tunnel in June. The mouth of the tunnel was caved-in completely by a near miss within 30 yards, and the results were such that the bomb, hitherto produced solely on the authority of Air Chief Marshal Freeman, was officially "adopted" by the Air Staff. '' Grand Slam'' Resurrected The operational ceiling of the Lancaster carrying a 12-000-lb bomb was at that .time 16,000 to 18,oooft and was insufficient to afford the necessary striking velocity to penetrate to depths which would produce the maximum pressure wave. Nevertheless, it was decided to resume work on the 10-ton bomb and to use it against the heavily protected V-weapon structures in France. Early in 1945 one of these monsters was aimed at the Bielefeld viaduct, a massive structure carrying a strategic railway. In two attacks within three weeks seven spans were destroyed by near misses, which, although producing craters, were, as the Air Ministry put it, '' well on the way to destroying structure by pressure-wave effects." Hundreds of tons of smaller bombs had been expended on the viaduct, but even
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