The Grand Slam (Earthquake) bomb was a very large bomb developed by the British aeronautical engineer Barnes Wallis in late 1944 for use against large and protected buldings and structures against which smaller bombs were ineffective. It weighed nearly ten tonnes and remains the heaviest conventional (non atomic) used in any conflict.
Most large Allied World War II aircraft bombs had very thin skins to maximise the weight of explosive which a bomber could carry. Barnes Wallis developed the Tallboy bomb as a bunker buster. When it was calculated that Avro Lancaster bombers could be modified - the Lancaster BI (Special) - to carry an even larger bomb, he redesigned it and managed to produced a much larger one. The design was very aerodynamic with a tail which caused it to spin. This allowed it to reach supersonic speeds as it fell. It had a much thicker case than the typical World War II bomb so that it would survive the impact of hitting a hardened surface. Its hardened casing was cast in a single piece in a sand mold, using a concrete core. When dropped onto compacted earth it would penetrate over 40 meters into the ground. The explosion would leave a 'cavern' which would undermine foundations of structures above causing collapse.
'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. In another attack against Valentin submarine pens near Bremen two Grand Slams penetrated 4 to 7 meters of reinforced concrete. They were also used successfully 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.
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: 2.36 t (5,200 lb) "Torpex D1" (Torpedo explosive)
Number used:41
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