text: Standard Avro Lancaster bombers could not carry the bomb; Avro built 32 Lancaster B.Mk 1 (Special)s with more powerful Merlin engine variants, a stronger undercarriage, without bomb bay doors and minus many items to save weight. 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; it 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 on impact or explode prematurely. The bombs had been designed to land in soft ground, penetrate deeply and then explode, creating a , 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 atomic 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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