Global conflict during World War II served as a catalyst for technological advances in many areas. As the video above describes, during WWI a twenty-pound bomb was considered large, and early in WWII, a 1,000-pound bomb was massive.
In 1941, a British aeronautical engineer named Barnes Wallis presented a paper entitled A Note on a Method of Attacking the Axis Powers. In that note, Wallis showed how a 10-ton bomb would weigh enough to penetrate deep underground, and if dropped close to a building, the bomb would function as an earthquake and transmit the explosive shockwaves into the building’s foundations. To make his idea feasible, Wallis also designed a new bomber capable of carrying such a heavy payload, but as the Air Ministry did not like the idea of a single-bomb aircraft, the idea was dropped.
After another of Wallis’ designs–the “bouncing bomb” for the Dam Busters of Operation Chastise–was used in 1942, the Ministry moved forward with building a smaller version of Wallis’ bomb. The resulting “Tallboy” bomb weighed in at 12,000 pounds, but Wallis’ original design had called for a bomb almost twice that size. After dozens of successes using the “Tallboy” throughout 1944–45, production moved forward on Wallis’ design for a 22,000-pound bomb, the “Grand Slam.”
The Grand Slam was also an earthquake bomb, and measuring in at 26-feet long, it was designed to penetrate concrete roofs. The bomb’s weight required that it be carried by a specially outfitted Avro Lancaster B.Mk 1. Gravity acting on such a large mass caused a falling Grand Slam bomb to reach near-supersonic speed (1,049 ft/s (715 mph)) before penetrating the target.
The first wartime use of the Grand Slam bomb came on 14 March 1945 when No. 617 Squadron RAF bombed the Schildesche viaduct in Bielefeld, Germany. The Grand Slam bomb, dropped from a height of 11,965 ft, left a crater 120 feet wide and 35 feet deep, and destroyed more than 100 yards of the viaduct. By the end of the War, the RAF had dropped 42 Grand Slam bombs, which had gained the nickname “Ten Ton Tess.” The Grand Slam is still the largest conventional weapon to have been deployed by the British military.