Grand Slam ( bomb ) The Grand Slam was a earthquake bomb used by RAF Bomber Command against strategic targets during the Second World War . Known officially as the Bomb , Medium Capacity , 22 , 000 lb , it was a scaled - up version of the Tallboy bomb and closer to the original size that the bombs ' inventor , Barnes Wallis , had envisaged when he first developed his earthquake bomb idea . It was also nicknamed " Ten ton Tess " . Development . On 18 July 1943 , work started on a larger version of the Tallboy bomb , which became the Grand Slam . As with the original Tallboy , the Grand Slam ' s fins generated a stabilizing spin and the bomb had a thicker case than a conventional bomb , which allowed deeper penetration . After the hot molten Torpex was poured into the casing , the explosive took a month to cool and set . Like the Tallboy , because of the low rate of production and consequent high value of each bomb , aircrews were told to land with their unused bombs on board rather than jettison them into the sea if a sortie was aborted . After release from the Avro Lancaster B . Mk 1 ( Special ) bomber , the Grand Slam would reach near - supersonic speed , approaching 1 , 049 ft / s ( 715 mph ) - ( 320 m / s , 1150 km / h ) , and penetrate deep underground , with the explosion causing a camouflet ( cavern ) and shifting the ground to undermine a target ' s foundation . Unlike the Tallboy , the Grand Slam had been designed to directly penetrate concrete roofs ; they tended to not detonate prematurely nor break up . This made them far more effective than any existing bomb . Grand Slam combat operations . By the end of the war , 42 Grand Slams had been dropped on active service . Post – war operations . Beginning in March 1946 , Project Ruby was a joint , Anglo – American project to investigate the use of penetration bombs against heavily – protected , concrete targets . The target selected was the Valentin submarine pens , that had been rendered unusable and abandoned since 617 Squadron ' s attack on 27 March 1945 . Grand Slams were carried by Lancasters from No . 15 Squadron RAF and US Boeing B - 29 Superfortress . Around 140 sorties were flown , testing a range of different bombs . Survivors . Four complete Grand Slam bombs are preserved and displayed in the United Kingdom at the RAF Museum , London , Brooklands Museum , RAF Lossiemouth and the Battle of Britain Memorial Flight Visitors ' Centre at RAF Coningsby . The main portion of a bomb , without the lightweight tail , is at the Kelham Island Museum in Sheffield . A live Grand Slam bomb was mistakenly displayed as a gate guardian at RAF Scampton for nearly fifteen years before the mistake was realised . It was gingerly removed ( by crane and low - loader ) to the test range at Shoeburyness , where it was detonated . A T - 14 bomb ( an American - made variant of the Grand Slam ) is displayed at the Air Force Armament Museum in the United States . Two Grand Slam bombs are in Pakistan , one each in Karachi and Sargodha . The bombs were in India , probably in transit to the Pacific theatre , when the war ended and remained there to be inherited by Pakistan on its creation by partition from India in 1947 .