Grand Slam bomb

A British 22,000 lb (10,000 kg) Grand Slam bomb

The Grand Slam earthquake bomb, was a very large freefall bomb developed by the British aeronautical engineer Barnes Wallis (who also made the bouncing bomb) in late 1944. It was a devlopment of, and at a weight of 9.98 t (22,000 lb), almost twice the weight of his previous large bomb, the 12,000 lb (5.44 t) Tallboy. Both weapons were intended for use against large and protected buildings, structures against which smaller bombs would be ineffective. The name grand slam comes from the game of bridge, where it is a term that means winning all the tricks, "cleaning the table".

Development history

The idea of the earthquake bomb was explored by Barnes Wallis at the very start of World War II (see Tallboy bomb for the principle of his "earthquake" bombs and their intended purpose in strategic warfare), but at the time there were no aircraft capable of carrying the 10-ton weapon he envisaged (notwithstanding Wallis's suggestions to that they were built, a six-engine high-altitude bomber design of his own called the "Victory Bomber"). Wallis returned to his designs in the latter part of the war and the first earthquake bomb he developed was the 5-ton Tallboy. It proved effective in demolishing large structures, including heavily-protected bunkers (it was thus an early "bunker buster").

The reasoning behind the earth penetration bomb is that explosive energy is transmitted more efficiently in a non-compressible medium. Barnes Wallis used the non-compressible nature of water as a factor in the bouncing bombs. The earthquake bomb was designed to penetrate the earth and explode some 30 m down. An explosion carried through the medium of the earth would thus cause damage for a much greater distance than if the bomb were to explode in open air. Wallis also understood that bomb aiming was very poor at the time. The major advantage of the earthquake bomb, therefore, was that it could miss by hundreds of yards and still achieve the desired result. The intention before the war started was to destroy dams, railway bridges and general infrastructure. Thus it is possible that German industry and infrastructure could have been seriously damaged with minimal loss of civilian lives, compared to area bombing. His ideas were not fully understood, appreciated, or even realisable at the time.

When it was calculated that the Avro Lancaster B1 Special bombers used for Tallboy could carry an even larger bomb, work started on the Grand Slam, which was effectively a scaled-up Tallboy. The new design was highly aerodynamic, with a long tail incorporating offset fins, causing it to spin as it fell and stabilizing it, due to the gyroscopic effect, much as the spin imparted by the rifling of a gun barrel increases the accuracy of a bullet. The spin also allowed the bomb to reach supersonic speeds, as the increased stability enabled it to pass through the sound barrier without wobbling or being thrown off-course.

The Grand Slam had a much thicker case than typical World War II bombs, so it would survive the impact of hitting a hardened surface. The hardened steel bomb casing was cast in one piece in a sand mould using a concrete core. Torpex was then poured in, bucket by bucket. When filled, the hot molten explosive took a month to cool down and set, greatly limiting production. Like the Tallboy, the rate of production and material and manpower investment in each bomb meant that aircrews were told to land with their unused bombs on board, rather than jettison them into the sea if a sortie was aborted.

When dropped from high altitude onto compacted earth, the Grand Slam would penetrate over 40 metres into the ground. The explosion would leave a camouflet (cavern) which would undermine foundations of structures above, causing collapse. This is what happened to the Bielefeld railway viaduct, the first enemy target destroyed by a Grand Slam.

Post-war the Handley Page Victor was designed with the provision to carry either a single Grand Slam, or two of the smaller Tallboys, internally.

The bomb was also built in the US where it was designated as "Bomb, GP, 22,000-lb, M110 (T-14)". The US developed a larger bomb using the same principles as the Grand Slam, the T-12 Cloudmaker, which weighed 20,000 kg (44,000 lb) , but it was not employed operationally.

Operational use

The Farge U-boat pen after being hit by a Grand Slam - note the figure standing on the pile of rubble.

The 'B1 (Special)' Lancaster bomber could only carry one at a time and it had to be dropped from 22,000 feet (6700 m) which limited its accuracy. The Grand Slam was first used on March 14, 1945 when the Royal Air Force No. 617 "Dambusters" Squadron, lead by Squadron Leader C.C. Calder, attacked the Bielefeld railway viaduct destroying two spans of the viaduct.^[1]

The viaduct at Arnsberg was bombed on 15 March 1945 with 2 Grand Slams and 14 Tallboy bombs but they failed to bring the viaduct down. Four days later on 19 March 1945 another attack by No 617 Squadron using 6 Grand Slams was successful and a 12 m (40 ft) gap was blown in the viaduct.^[1]

Farge is a small port on the Weser River north of Bremen, and was the site of an oil-storage depot and the Valentin submarine pens that were attacked by the RAF on 27 March 1945. The pens had a ferrous concrete roof up to 7 metres (23 feet) thick. Two Grand Slam bombs penetrated parts of the pen with a 4.5 m-thick roof^[2][3]

Grand Slams were also successfully used against the Huuge and Brest submarine pens. By the end of the war 41 Grand Slam bombs had been dropped, mainly against bridges and viaducts.

Marshal of the Royal Air Force Sir Arthur Harris GCB OBE AFC RAF, of RAF Bomber Command wrote in 1947 that:

We already had Wallis's 12,000 lb. [Tallboy] medium capacity bomb, which was capable of breaking through the roof of a railway tunnel or a very thick concrete roof, and when the success of this bomb was proved Wallis designed a yet more powerful weapon, the 22,000 lb. bomb, the most destructive missile in the history of warfare until the invention of the atom bomb. This 22,000 lb. Bomb did not reach us before the spring of 1945, when we used it with great effect against viaducts or railways leading to the Ruhr and also against several U-boat shelters.

Characteristics

Footnotes and references

1. ^ ^{a b} http://www.raf.mod.uk/bombercommand/mar45.html RAF: Bomber Command Campaign diary: March 1945]
2. ^ RAF: Bomber Command: Grand Slams
3. ^ http://www.lostplaces.de/cms/marine/uboot-bunker-valentin-bremen-farge.html German site

See also

• Nuclear bunker buster
• GBU-43 Massive Ordnance Air Blast bomb
• GBU-28
• BLU-82
• T12

Further reading

• 617 attacked the Bielefeld railway viaduct
• Grand Slam bomb from WW2 (J Mullen)
• A live Grand Slam that survived in plain sight until 1958
• English Bombs of WWII
• Code Named "Aphrodite"
• Bombs Weapons Rockets Aircraft Ordnance
• Guinness world records
• camouflet
• Picture of the destroyed Arnsberg viaduct (German language site)
• A picture of a Grand Slam being released

Donate to Wikimedia