Tallboy (bomb)
Tallboy or Bomb, Medium Capacity, 12,000 lb was an earthquake bomb developed by the British aeronautical engineer Barnes Wallis and used by the Royal Air Force during the Second World War.
At, it could be carried only by a modified model of the Avro Lancaster heavy bomber. It proved to be effective against large, fortified structures where conventional bombing had proved ineffective.
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, which would fly at at to carry the heavy bomb over, but the Air Ministry opposed a single-bomb aircraft, and the idea was not pursued after 1942.
The design and production of Tallboy was undertaken 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. The RAF therefore used bombs which they had not purchased and which therefore remained the property of Vickers, the manufacturer. This situation was normalised once the weapon’s capabilities were established.
Accomplishments of the Tallboy included the 24 June 1944 Operation Crossbow attack on La Coupole 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 below the surface.
The last of the Kriegsmarine's Bismarck-class battleships, the Tirpitz, was sunk by an air attack using Tallboys in Operation Catechism.
Design
Most large Allied, particularly British, Second World War 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 bombs was low.To be able to penetrate the earth 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 aerodynamically clean so that, when dropped from a great height, it would reach a much higher terminal velocity 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 of the overall length. Initially, the bomb had a tendency to tumble and 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, improving aerodynamics and accuracy.
The Tallboy was designed to be dropped from an optimal altitude of at a forward speed of, hitting at. It made a crater deep and across and could go through of concrete.
The weight of the Tallboy 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.
No. 617 Squadron were trained on the Stabilizing Automatic Bomb Sight. Corrections had to be made for temperature, wind speed and other factors. The sight was effective only if the target could be clearly identified. Several missions were cancelled or unsuccessful because of this limitation.
For use on underground targets, the bomb was fitted with three separate inertia No. 58 Mark I Tail 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.
To guarantee detonation, three 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, the third would trigger detonation. At least 2 Tallboys failed to explode, one during the second attack on the Sorpe dam; it was found during repairs in late 1958 when the reservoir was emptied, and a second was found in Świnoujście in Poland in 2020. This second bomb detonated in October 2020 while being remotely defused.
The bomb 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 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 surroundings, with the blast dissipating rapidly through the air. An earthquake impact shook the whole target and caused structural damage to all parts of it, making repair uneconomic.
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 a crater with depths up to, 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
Tallboys were largely hand-made, requiring much labour during each manufacturing stage. The materials used were costly, with precise engineering requirements in casting and machining. To increase penetrative power, a large, 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 perfectly symmetrical 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 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 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.
Operations
June–August 1944
- Nineteen Tallboy-equipped and six conventionally equipped Lancasters of 617 Squadron attacked a railway tunnel near Saumur on the night of 8/9 June 1944. This tunnel was expected to be used for the movement of a German Panzer unit. 617 Squadron were guided on to the target by 83 Squadron Pathfinder Force. This was the first use of the Tallboy bomb, and the line was destroyed—one Tallboy bored through the hillside and exploded in the tunnel about below, completely blocking it. No aircraft were lost during the raid.
Operation Crossbow
19 June 1944 – Watten
- The nearest Tallboy dropped by 617 Squadron landed from the target, a heavily fortified V-2 launch site under construction The bunker was rendered useless.
- The target was a V-2 assembly and launch site linked with the Watten site. Several Tallboy hits undermined the foundations but did not penetrate the dome. The bunker was abandoned.
- Lancasters of 617 Squadron scored three direct hits with Tallboys without loss.
- 617 Squadron used seventeen Lancasters with Tallboys, supported by one Mosquito and one Mustang, in an attempt to collapse the limestone roof of the caves used as storage depots. Aircraft from No 5 Group followed up with bombs.
- Attack on V-weapon targets. Damage was unknown at the time, and efforts continued. In September, allied ground forces found galleries blocked with earth and debris where Tallboys had hit one of the shafts. The V-weapon was revealed to be the V-3 cannon.
- 16 Lancasters, led by a Mosquito and a Mustang, bombed Wizernes – three Lancasters managed to drop Tallboys.
- One Tallboy hit the target but did not penetrate the structure.
- Both ends of the railway tunnel were collapsed by Tallboys dropped by 617 Squadron. William Reid's Lancaster at was hit by a 'friendly' Tallboy dropped from.
Sorties against German dockyards
14 June 1944 – Le Havre
- Part of the first massive RAF daylight raid since the end of May 1943, two waves attacked E-boat facilities at Le Havre: No 1 Group first, No 3 Group second. Just before the first wave, 22 Lancasters of 617 Squadron and 3 Mosquito marker aircraft attacked, several hits were scored on the pens, one bomb penetrated the roof.
- 297 aircraft: 155 Lancasters, 130 Halifaxes, 12 Mosquitos, of Nos 1, 4, 5, 6 and 8 Groups attacked Boulogne harbour. One Halifax was lost. A French report described the great destruction as the worst raid on Boulogne. During the raid 22 Lancasters of No. 617 squadron bombed the E-boat pens with Tallboys. Due to cloud cover ten planes returned to base with their bombs. However, the raid was considered a success as the E-boats retired to IJmuiden on the Dutch coast, where they were better protected but less able to interfere with Allied naval traffic supporting the Normandy invasion.
- 15 Lancasters of 617 Squadron attacked the U-boat pens at Brest and scored six direct hits with Tallboys, penetrating the concrete roofs. One Lancaster was shot down by flak. Subsequent attempts to reinforce other sites with even thicker concrete diverted resources from other projects.
- Flight Lieutenant Thomas Clifford Iveson dropped one Tallboy, bomb failed to penetrate base.
- The planned Tallboy mission against the U-boat pens was cancelled. Instead Keroman Submarine Base was the primary target.
- Flight Lieutenant Thomas Iveson dropped one Tallboy.
- Iveson dropped one Tallboy.