Type Earthquake bomb Wars World War II | Place of origin United Kingdom Designer Barnes Wallis | |
 | ||
In service 8 June 1944 – 25 April 1945 Used by No. 9 Squadron RAF, No. 617 Squadron RAF | ||
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, at five long tons and carried by the Avro Lancaster. It was effective against hardened structures against which prior, smaller bombs had proved ineffective.
Contents
History
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 ft (14,000 m) to carry the heavy bomb over 4,000 mi (6,400 km), but the Air Ministry opposed a single-bomb aircraft, and the idea was not pursued after 1942.
The design and production of Tallboy was done without a contract on the initiative of the Ministry, following Wallis' 1942 paper Spherical Bomb—Surface Torpedo and the design of the "bouncing bomb" for the Dam Busters of Operation Chastise. As such, the RAF used bombs that they had not bought and which were still the property of Vickers the manufacturer. This situation was normalised once their capabilities were recognised.
Accomplishments of the Tallboy included the 24 June 1944 Operation Crossbow attack on La Coupole—along with Grand Slams—which undermined the foundations of the V-2 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 ft (18 m) below the surface.
The last of the Kriegsmarine's Bismarck-class battleships the Tirpitz was sunk by an air attack using Tallboys.
Design
Most large Allied World War II aircraft bombs had very thin skins to maximize the weight of explosive that 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 terminal velocity much higher than traditional bomb designs.
In the final design, the No. 78 Mark I tail of the bomb was about half the overall length of the finished weapon; the bomb casing was some 10 ft (3.0 m) of the overall 21-foot (6.4 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.
Tallboy was designed to be dropped from an optimal altitude of 18,000 ft (5,500 m) at a forward speed of 170 mph (270 km/h), hitting at 750 mph (1,210 km/h). It made a crater 80 ft (24 m) deep and 100 ft (30 m) across and could go through 16 ft (4.9 m) of concrete.
The weight of the Tallboy (approximately 12,000 lb (5.4 t)) 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.
At the same time, No. 617 "Dambusters" Squadron were 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 No. 58 Mark I Tail 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.
The bomb was aimed at the target during an operation and proved capable of penetrating deep into hardened reinforced concrete when it hit. This, however, was not the primary intention of Barnes Wallis's design. The bomb was designed to make impact close to the target, penetrate 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 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.
An alternative technique was to arrange detonation depth so that the crater broke the surface—useful for attacking railway marshalling yards and similar targets. The Tallboy produced an 80 ft crater with depths up to 100 ft, unlike conventional bombs which would produce many shallow craters across a target—each one of which could later be filled in rapidly with earth-moving equipment. Such a huge hole was time-consuming to fill; multiple trucks and bulldozers could not be fitted around the periphery of the hole to speed the process.
Manufacturing
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.
The Torpex filling was poured by hand into the base of the upturned casing after melting it in "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 (100 mm) layer of woodmeal-wax composite with three cylindrical recesses fitted with the explosive boosters and into which three chemical time-fuses were inserted when the bomb was finally armed.
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. 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.
June – August 1944
Operation Crossbow sorties
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, Tallboys were deployed on a number of sorties by the British to destroy several missile sites.
Sorties against German dockyards
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.
September – November 1944
Bombing sorties against Tirpitz
The German battleship Tirpitz was a threat against convoys sailing to and from the Soviet Union.
December 1944 – April 1945
Bombing of U-boat pens, December 1944 – April 1945
617 Squadron.
The viaducts were attacked by 617 and 9 squadrons with Tallboys and the first Grand Slams. The Arnsberg viaduct withstood the attack but 100 m (330 ft) of the Bielefeld viaduct collapsed through the 'earthquake effect' of the Grand Slams and Tallboys.
The Lützow was attacked by 617 Squadron. Despite intense flak, 15 aircraft managed to bomb the target with Tallboys or with 1,000-pound (450 kg) bombs. 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.
Hitler's vacation home, the Berghof, near Berchtesgaden was attacked with a mixed force that included six Lancasters of 617 Squadron dropping their last Tallboys. The bombing appeared to be accurate and effective.
Post War
The latter of the V bombers – the Handley Page Victor – was designed to be able to carry a bomb load that could include a load of two Tallboys internally, or one Grand Slam plus assorted smaller weapons.
Use by the United States
The T-10 was an American-made version of the 12,000 pounds (5,400 kg) 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, since the capitulation of Japan following the atomic bombings of Hiroshima and Nagasaki negated their need. In the late 1950s the T-10 was re-designated the M-121. During the Korean War a number of T-10s were converted to the radio guided Tarzon bomb and were used to destroy railroad bridges and reservoir dams, being dropped by the Boeing B-29 Superfortress.
After the Korean War ended and the B-29 and B-36 bombers were retired, the United States Air Force 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. During the Vietnam War, some M-121s, minus their rear streamlined shrouds and tail fin assemblies were shipped to Vietnam for Commando Vault missions where the warheads were incorporated into the BLU-82 weapons dropped by C-130s using radar control. The warheads were mounted on a platform and pulled by parachutes from the rear loading ramp of C-130s. After clearing the aircraft the large extraction chutes and pallets were cut away and small triangular chutes stabilized the large warhead until impact. A three-foot nose probe detonated the bomb at the correct stand-off distance. One of the last of the World War II Tallboy designs was dropped during a Commando Vault mission to clear a landing zone for helicopters on a ridge during the 1969 Battle of Hamburger Hill in Vietnam. Dropping from 3,000 metres (10,000 ft), the bomb hit exactly where it was needed. The Commando Vault missions were more accurate in bomb delivery on target than the more modern B-52s.
Work still progressed on the 43,000 lb (20,000 kg) T-12 Cloudmaker, which could be carried by the Convair B-36A.