| Tallboy | |
|---|---|
Modern replica of a Tallboy |
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| Type | Conventional |
| Place of origin | United Kingdom |
| Service history | |
| In service | 8 June 1944 - 25 April 1945 |
| Used by | No. 617 Squadron RAF |
| Wars | World War II |
| Production history | |
| Designer | Barnes Wallis |
| Manufacturer | Vickers |
| Number built | 854[1] |
| Specifications | |
| Weight | 5,443 kg (12,000 lb) |
| Length | 6.35 m (21 ft) |
| Diameter | 950 mm (38 in) |
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| Filling | Torpex D1 |
| Filling weight | 2,358 kg (5,200 lb) |
| Detonation mechanism |
No. 58 fuse - built from No. 30 Pistol (impact detonation) - or No. 47 time delay fuze. Fuses were inserted into tetryl boosters. |
The Tallboy or Bomb, Medium Capacity, 12,000 lb, was an earthquake bomb developed by the British aeronautical engineer Barnes Wallis and deployed by the RAF in 1944. It weighed five tons and, carried by the Avro Lancaster, was effective against hardened structures against which earlier, smaller bombs had proven ineffective.
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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 are transmitted through the ground more strongly than through air.
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 aircraft 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 design and production of Tallboy was done without a contract on the initiative of the Ministry. As such, the RAF were using bombs they had not bought and that were still the property of the manufacturers, Vickers. This situation was normalised once their capabilities were recognised.
Accomplishments of the Tallboy included: 24 June 1944, Operation Crossbow attack on La Coupole (along with Grand Slams), which undermined the foundations of this V2 assembly bunker and a Tallboy attack on the Saumur tunnel on 8-9 June 1944, when bombs passed straight through the hill and exploded inside the tunnel 60 feet (18 m) below the surface.[2]
The last of the Kriegsmarine's Bismarck-class battleships, the Tirpitz, was sunk by an air attack using Tallboys.
Most large Allied World War II aircraft bombs had very thin skins to maximize the weight of explosive a bomber could carry—this was an improvement on the early part of the war when the explosive 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.
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]
It was an extraordinary weapon, an apparent contradiction in terms, since it had at one and the same time the explosive force of a large high-capacity blast bomb and the penetrating power of an armour-piercing bomb. On the ground it was capable of displacing a million cubic feet (29,000 m³) of earth and made a crater which it would have taken 5,000 tons of earth to fill. It was ballistically perfect and in consequence had a very high terminal velocity, variously estimated at 3,600 and 3,700 feet (1,100 m) per second (1,100–1,130 m/s or about 2,500 mph / 4,000 km/h), which was, of course, a good deal faster than sound so that, as with the V-2 rocket, the noise of its fall would be heard after that of the explosion.
The weight of the Tallboy (approximately 12,000 lb) and the high altitude required of the bombing aircraft meant that the Avro Lancasters 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, and other factors. It was only effective if the target could be identified and several missions were cancelled 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 (firing mechanisms). 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.
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 fuses failed to function, the third would trigger detonation. Despite this elaborate system, at least one Tallboy failed to explode during the second attack on the Sorpe dam and was found during repairs in late 1958 when the reservoir was emptied.
Although the bomb was aimed at the target during an operation, and proved capable of penetrating deep into hardened reinforced concrete when it 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 beneath or around the target, and then detonate, transferring all of its energy into the structure, or creating a camouflet (cavern or crater) into which the target would fall.
This 'earthquake' effect caused more damage than even a direct hit that 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, to increase penetrative power, a large and specially hardened steel plug had 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 to ensure optimum aerodynamic performance. This was no easy task when manipulating a bomb casing with the size and weight of a Tallboy.
Similarly, the Torpex filling was poured into the base of the upturned casing by hand, after melting it in explosives "kettles". The final stage of explosive filling required that a one inch layer of pure TNT be poured over the Torpex filling, followed by sealing the base with a 4 inch layer of woodmeal-wax composite with three cylindrical recesses fitted with the explosive boosters and into which (when the bomb was finally armed), a total of three chemical time-fuses were inserted.
Tallboys were not considered expendable, and if not used on a raid were to be brought back to base rather than safely jettisoned into 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 that 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.
Operation Crossbow was a set of offensive and defensive measures that were carried out to deal with the threat of the German V-1 flying bomb ("buzz bomb" or "doodlebug") and V-2 rocket weaponry. As part of the operation, a number of sorties using Tallboys were deployed by the British to destroy several missile sites.
Shipping 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.
The German battleship Tirpitz was a threat against convoys sailing to and from the Soviet Union.
IJmuiden, 12 January 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 as American troops advanced. The lip of the dam was damaged, but the Germans prevented further damage by lowering the water level.[17][18]
Politz was attacked by 617 Squadron on 21 December 1944[19]
The Bielefeld and Arnsberg viaducts were attacked by 617 and 9 squadrons with Tallboys and the first Grand Slams 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 Slams and Tallboys.[4] The Arnsberg viaduct was attacked again on 15 March 1945 by 9 Squadron, it did not collapse.[4]
The Pocket battleship Lützow was attacked on 16 April 1945 by 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 of the war.[4]
Hitler's vacation home, Berghof, near Berchtesgaden was attacked on 25 April 1945 with a mixed force that included six Lancasters of 617 Squadron dropping their last Tallboys. The bombing appeared to be accurate and effective.[4]
The T10 was an American-made version of the 12,000 lb Tallboy modified to use standard American components. Development was started in late 1944 and plans were made to drop them on the fortified island strongholds of the Pacific to aid in softening their defences before amphibious assaults. None were ever used in combat because the capitulation of Japan following the atomic bombings of Hiroshima and Nagasaki negated their need. Later in the late 1950s the T-10 was re-designated the M-121. Later during the Korean War a number of T-10s were converted to the radio guided Tarzon bomb and was used to destroy railroad bridges and reservoir dams, being dropped by the B-29 Super Fortress.[20]
After the Korean War ended and the B-29 and B-36 bombers were retired the USAF no longer had an aircraft that could drop the completely assembled M-121 and they were put in storage. Production of the T-10 ended in 1955. The B-36 was the last operational aircraft that could drop a fully assembled Tallboy type bomb in the conventional way. [21] During the Vietnam War, some M-121s, minus their rear streamline shroud and tail fin assembly were shipped to Vietnam for Commando Vault missions where the warhead was dropped by C-130 using radar control. The warhead was mounted on a platform and pulled by a parachute from the rear loading ramp of the C-130. After clearing the aircraft the large extraction chute and pallet were cut away and small triangular chute stabilized the large warhead till impact. A three foot nose probe detonated the bomb at the right stand-off. One of the greatest missions for the last of the World War Two Tallboy designs was the dropping of one on a Commando Vault mission to clear a landing zone for helicopters on a ridge during the famous Battle of Hamburger Hill. Dropping from 10,000 feet the bomb hit exactly where it was needed. In reality the Commando Vault missions were more accurate in bomb delivery on target than the more modern B-52s.[22][23]
Work still progressed on the 43,000 lb (20,000 kg) T-12 Cloudmaker, which the B36 Peacemaker had been redesigned to deploy.
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