Grand Slam (bomb)
The Grand Slam (Earthquake) bomb was a very large bomb developed by the British aeronautical engineer Barnes Wallis in late 1944. The Grand Slam bomb was twice the weight of his previous large bomb, the Tallboy; both weapons were intended for use against large and protected buildings, and structures against which smaller bombs would be ineffective. The Grand Slam weighed nearly ten tonnes.
Development history
The idea of the earthquake bomb was explored by Barnes Wallis at the very start of the war (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 build one). 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 (an early "bunker buster").
When it was calculated that the Avro Lancaster BI 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, 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 mold using a concrete core. The explosive charge 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 onboard, 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 meters 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.
The reasoning behind this earth penetration bomb, is that explosive waves transmitt power more effeciently in a non compressible medium. Barnes wallace used the non-compressibilty of water as a factor in the bouncing bombs. Air is compressible and thereofre wastes a great deal of explosive power. Barnes originally designed these bombs to destroy damns, railway bridges and general infrastructure, but his ideas were not fully understood or appreciated by those in government at the time. Thus the bombs were used against speciallised targets and not in the manner they were desingned for.
Operational use
The 'BI (Special)' Lancaster bomber could only carry one at a time and it had to be dropped from 22,000 feet 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 Slam 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 7 metres (23 feet) thick which was penetrated by 2 Grand Slam bombs.[2]
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.
Arthur Harris 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.
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 US developed a larger bomb using the same principles as the Grand Slam, the T-12 Cloudmaker, which weighed 44,000 pounds (20,000 kg), but it was not employed during the war.
Characteristics
- Length: 7.70 m (26 ft 6 in)
- Tail: 4.11 m (13 ft, 6 in)
- Diameter: 1.17 m (3 ft, 10 in)
- Weight: 9.98 t (22,000 lb)
- Warhead: 4,144 kg (9,135 lb) "Torpex D1" (Torpedo explosive)
- Number used:41
Further reading
- 612 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)
Footnotes
- ^ a b http://www.raf.mod.uk/bombercommand/mar45.html RAF: Bomber Command Campaign diary: March 1945]
- ^ RAF: Bomber Comand: Grand Slams