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The Tallboy was an earth quake bomb developed by Barnes Wallis and brought into operation by the British in 1944. It weighed five tons and, carried by the Avro Lancaster bomber, was effective against hardened structures against which earlier, smaller bombs had proved ineffective.
[edit] HistoryThe British aeronautical engineer Barnes Wallis presented his ideas for a 10 ton bomb in his 1941 paper A Note on a Method of Attacking the Axis Powers, which showed that a very large bomb exploding deep underground next to a target would transmit the shock into the foundations of the target, particularly since shock waves transmitted through the ground are less attenuated than through air. Barnes Wallis designed the "Victory Bomber" of 50 tons which would fly at 320 mph (510 km/h) at 45,000 feet (14,000 m) to carry the heavy bomb over 4,000 miles (6,400 km), but the Air Ministry were against a single-bomb bomber and the idea was not pursued beyond 1942. Following Wallis's 1942 paper Spherical Bomb — Surface Torpedo and the design of the "bouncing bomb" for the Dam Busters of Operation Chastise, the actual design and production of Tallboy was done without a contract on the initiative of a single official within the Ministry. As such the RAF were using bombs they had not bought and which were actually still the property of the manufacturers; Vickers. This situation was regularized once their capabilities were recognised. Amongst many spectacular accomplishments by the Tallboy, the June 24, 1944 Operation Crossbow attack on the La Coupole (along with Grand Slam bombing) undermined the foundations. A Tallboy of the June 8/9, 1944 Saumur tunnel attack passed straight through the hill and exploded right inside the tunnel 60 feet (18 m) below the surface.[2] The last Kriegsmarine Bismarck class battleship, the Tirpitz, was sunk by an air attack using Tallboys. [edit] DesignMost large Allied World War II aircraft bombs had very thin skins to maximize the weight of explosive which a bomber could carry—this was an improvement on the early part of the war when the actual HE content of British bomb designs was low. To be able to penetrate the earth (or hardened targets) without breaking apart, the casing of the Tallboy had to be strong. Each was cast in one piece of high tensile steel that would enable it to survive the impact before detonation. At the same time to achieve the penetration required, Wallis designed the Tallboy to be very aerodynamic so that when dropped from a great height it would reach a velocity higher than traditional bomb designs. In the final design the tail of the bomb was about half the overall length of the finished weapon—the bomb casing was some 10 feet (3 m) of the overall 21-foot (6 m) length. Initially the bomb had a tendency to tumble, so the tail was modified—the fins were given a slight twist so that the bomb spun as it fell. The gyroscopic effect thus generated stopped the pitching and yawing, improved the aerodynamics and improved accuracy. The improved design worked so well that it was found in development that it passed through the sound barrier as it fell.[citation needed] When dropped from 20,000 ft (6,100 m) it made a crater 80 feet deep (24 m) and 100 feet (30 m) across and could go through 16 feet (5 m) of concrete.[1] W. J. Lawrence wrote about the Tallboy bomb in his book, No 5 Bomber Group:[3]
The weight of the Tallboy (approximately 12,000 lb) and the high altitude required of the bombing aircraft meant that the Lancaster bombers used had to be specially adapted. Armour plating and even defensive armament were removed to reduce weight and the bomb-bay doors had to be adapted. Even then the Lancaster was not capable of reaching the bomb's intended dropping height of 40,000 ft (12,200 m) but only around 25,000 (7,700 m). At the same time No. 617 "Dambusters" Squadron trained in the use of a special bombsight the Stabilizing Automatic Bomb Sight (SABS). For accuracy multiple corrections had to be made for temperature, wind speed, etc. However it was only effective if the target could be identified and several missions were canceled or unsuccessful because of difficulty in accurately identifying and marking the targets. For use on underground targets, the bomb was fitted with three separate inertia pistols. These triggered detonation after a pre-set delay, which gave the bomb sufficient time to penetrate the target before exploding. Depending on mission requirements, the time delay could be set to 30 seconds or 30 minutes after impact. In order to guarantee detonation, a total of three separate Type 47 long delay fuzes were fitted inside the rear of the bomb. This dramatically improved reliability of the weapon: even if two of the fuzes failed to function, the third would trigger detonation. Although the bomb was aimed at the target during an operation, and proved capable of penetrating amazing depths into hardened reinforced concrete when it did hit, this was not the primary intention of Barnes Wallis's design. The bomb was designed to impact close to the target, slide into the soil or rock on which the target was built, and then detonate, transferring all of its energy into the structure, or creating a camouflet into which it fell. This 'earthquake' effect caused more damage than even a direct hit which penetrated the armour of a target, since even a burst inside a bunker would only damage the immediate surroundings, with the blast dissipating rapidly through the air. An earthquake impact, however, shook the whole target, and caused major structural damage to all parts of it, making repair uneconomic. The attack reports below should be considered with this in mind. The construction of each Tallboy was labour intensive because each was largely hand-made, requiring much manual labour during each separate manufacturing stage. The materials used were costly, with very precise engineering requirements with regard to casting and machining. For example, in order to increase its penetrative power a large and specially hardened steel plug needed to be precisely machined and mated to a recess in the nose of the bomb. The ogive had to be machined into a perfectly symmetrical shape in order to ensure optimum aerodynamic performance. This was no easy task when manipulating a bomb casing with the size and weight of Tallboy. Similarly, the Torpex filling was poured into base of the upturned casing by hand, after melting it in explosives "kettles". The final stage of explosive filling required a one inch layer of pure TNT to be poured over the Torpex filling, followed by sealing the base with a 4 inch layer of woodmeal-wax composite with 3 recesses into which the explosive boosters and fuzes were fitted. Tallboys were not considered expendable and if not used on a raid were to be brought back to base rather than safely dropped in the sea.[4] The value of the weapon offset the additional risk to the aircrew. Given their high unit cost, Tallboys were used exclusively against high-value strategic targets which could not be destroyed by other means. When it was found that the Lancaster could be modified to carry a bomb larger than the Tallboy, Wallis produced the even larger Grand Slam bomb. [edit] Tallboy operations[edit] June - August 1944
[edit] Operation Crossbow sortiesOperation Crossbow was a set of offensive and defensive measures that were carried out to deal with the threat of German V-1 and V-2 rocket weaponry. As part of the operation, a number of bombing sorties that carried Tallboy bombs were deployed by the British to bomb and destroy a number of missile sites.
[edit] Sorties against German dockyardsShipping in the English Channel and the Atlantic Ocean were threatened by U-boats and E-boats stationed in France. U-boat docks were protected against conventional aerial bombardment by thick concrete roofs.
[edit] September - November 1944
[edit] Bombing sorties against TirpitzThe German battleship Tirpitz was a threat against convoys sailing to and from the Soviet Union.
[edit] December 1944 - April 1945
The Urft Dam, (30 miles south west of Cologne) was attacked on 8 December and 11 December 1944 to prevent it being used to flood the area below as American troops advanced. The lip of the dam was damaged, but the Germans prevented further damage by lowering the water level.[14][15] Politz was attacked by No. 617 21 December 1944[citation needed][16] The Bielefeld and Arnsberg viaducts were attacked by No. 617 and No. 9 squadrons with Tallboys and the first Grand Slam bomb on 14 March 1945. The Arnsberg viaduct withstood the attack but 100 m of the Bielefeld viaduct collapsed through the 'earthquake effect' of the Grand Slam and Tallboys.[4] The Arnsberg viaduct was attacked again on 15 March 1945 by No. 9 Squadron it did not collapse.[4] The Pocket battleship Lützow was attacked on 16 April 1945 by No. 617 Squadron. Despite intense flak, 15 aircraft managed to bomb the target with Tallboys or with 1,000-pounders. One near miss with a Tallboy tore a large hole in the bottom of the Lützow and she settled to the bottom in shallow water. One Lancaster was shot down, the Squadron's last loss in the war.[4] Hitler's vacation home, Berghof, near Berchtesgaden was attacked on 25 April 1945 with a mixed force which included 6 Lancasters of No. 617 Squadron dropping their last Tallboys. The bombing appeared to be accurate and effective.[4] [edit] See also[edit] Notes and references
[edit] External links
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