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 (RAF) during the Second World War.
At , it could only be carried by a modified model of the Avro Lancaster heavy bomber. It proved to be effective against large, fortified structures against which 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 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. The RAF used bombs that they had not bought and remained 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 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 (blockbuster 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 (or fortified 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 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 (approximately ) 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 (SABS). 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, 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 (formerly Swinemünde) in 2020. While being remotely defused, this second bomb detonated in October 2020.
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 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. 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 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.
Tallboy operations.
June – August 1944.
Operation Crossbow.
Crossbow was the code name for measures to counter the German V-1 flying bomb ("buzz bomb" or "doodlebug") and V-2 rocket weapons. Tallboys were used by the British to destroy several missile sites.
19 June 1944 – Watten
24 June 1944 – Wizernes
25 June 1944 – Siracourt V-1 bunker
4 July 1944 – Saint-Leu-d'Esserent
6 July 1944 – Mimoyecques
17 July 1944 – Wizernes
27 July 1944 – Watten
31 July 1944 – Rilly La Montagne
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.
14 June 1944 – Le Havre
15 June 1944 – Boulogne harbour
5 August 1944 – Brest
6 August 1944 – Keroman
7 August 1944 – Lorient
8 August 1944 – La Pallice
28 August 1944 – IJmuiden
September – November 1944.
23/24 September 1944 – Dortmund-Ems Canal near Ladbergen, north of Münster
7 October 1944 – Kembs Dam north of Basle
15 October 1944 – Sorpe dam
Bombing sorties against "Tirpitz".
The German battleship Tirpitz was a threat against convoys sailing to and from the Soviet Union.
15 September 1944 – (Operation Paravane)
29 October 1944 – (Operation Obviate)
12 November 1944 – (Operation Catechism)
December 1944 – April 1945.
Bombing of [U-boat]] pens, December 1944 – April 1945
15 December 1944 – IJmuiden on the Dutch coast,
12 January 1945 – Bergen
3 February 1945 – IJmuiden & Poortershaven
9 April 1945 – Hamburg
18 April 1945 – Heligoland
19 April 1945 – Heligoland
8 December, 11 December 1944
21 December 1944 – Politz
14 March 1945 – Bielefeld and Arnsberg viaducts
15 March 1945 – Arnsberg viaduct
16 April 1945 – pocket battleship "Lützow"
25 April 1945 – Berghof
Post war.
The last 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.
Unexploded ordnance.
In October 2020, a Tallboy bomb was found in the Piast Canal in northwest Poland near the town of Świnoujście and scheduled for defusing. The bomb had been dropped in the April 1945 attack on the "Lützow", a German cruiser. The Tallboy wound up detonating during a deflagration operation, but there were no reported injuries to divers nor any damage to the port infrastructure from the underwater explosion.
United States use.
The T-10 was an American-made version of the Tallboy modified to use standard American components. Development was started in late 1944 and plans were made to drop them on the island strongholds of the Pacific to aid in softening their defences before amphibious assaults. No bombs were used operationally 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 dropped by Boeing B-29 Superfortresses to destroy railroad bridges and reservoir dams.
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 M-121, and the bombs 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 in order to clear a helicopter landing zone. 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 , 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 T-12 Cloudmaker, which could be carried by the Convair B-36A.
References.
, July 1944
, August 1944
, September 1944
, October 1944
,November 1944
, December 1944
, January 1945
, February 1945
, March 1945
, April and May 1945)