22lb

The Bomb, Medium Capacity, 22,000 lb (Grand Slam) was a 22,000 lb (10 t) earthquake bomb used by RAF Bomber Command against German targets towards the end of the Second World War. The bomb was originally called Tallboy Large until the term Tallboy got into the press and the code name was replaced by "Grand Slam". The bomb was similar to a large version of the Tallboy bomb but a new design and closer to the size that its inventor, Barnes Wallis, had envisaged when he developed the idea of an earthquake bomb.
Medium Capacity (M.C.) bombs were designed to remedy the shortcomings of General Purpose (G.P.) bombs, with a greater blast and casings which were robust enough to confer a considerable capacity to penetrate, especially the Tallboy and Grand Slam. The Grand Slam case was made of a chrome-molybdenum alloy steel and had a charge-to-weight ratio of over 43 per cent.
Conventional Avro Lancaster bombers could not carry the bomb and 32 Lancaster B.Mk 1 (Special)s with more powerful engines, a stronger undercarriage, without bomb bay doors and minus many items to save weight, were built. When airborne with the Grand Slam a Special could barely manoeuvre and pilots were advised to refrain from minor adjustments of the flying controls, allowing the aircraft to wallow. A Lancaster which returned with its bomb was not permitted to land at RAF Woodhall Spa, the 617 Squadron base, but had to use the longer runway at RAF Carnaby.
From 14 March to 19 April 1945, 42 Grand Slams were dropped on Germany. When landing on reinforced concrete, the bombs tended to break up when they hit or explode prematurely. The bombs had been designed to land in soft ground, penetrate deeply and then explode, creating a camouflet, causing the structure above to subside. Grand Slams and Tallboys were capable of causing damage that smaller bombs could not, accelerating the collapse of German resistance and avoiding mass civilian casualties. Grand Slams were the most effective bombs used by the Allies until the advent of nuclear weapons later that year. After the war, the Royal Air Force and United States Army Air Forces used Grand Slams and other bombs for research.

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