Grand Slam ... The earthquake bomb.

The successful use of Tallboy led to the Ministry of Aircraft Production giving the go-ahead on 12th July 19441 for the production of a larger (22,000lb) variant, codenamed Grand Slam, for delivery in early 19451 (development had earlier been put on hold while efforts were concentrated on Tallboy) - this was the ten-ton deep penetration bomb conceived by Wallis five years earlier. Its greater size required further development of the special steel alloy for the casing, and meant that few places could machine the casing (it took two days for the initial casting to cool sufficiently for machining)! Although on paper well above the maximum load for a Lancaster, special modifications including the removal of gun turrets allowed the aircraft to carry Grand Slam up to the required 25,000 ft drop height (its greater size meant also that the Lancasters' bomb bay doors had to be removed entirely).
Its first use was against the Bielefeld Viaduct - 3,000 tons of bombs (including Tallboys) had already been dropped on it with little result, but Grand Slam brought it down on 14th March 19454 (the first Grand Slam had been test dropped in the New Forest the day before). Grand Slam was used against similar targets to Tallboy (often a raid would include both types of bomb), and again caused remarkable destruction wherever it was used - the Arnsberg, Arbergen, Neinburg and other bridges were also to be felled by the bomb. In total, 41 Grand Slams were dropped during the war. Photo reconnaissance records were kept of Tallboy and Grand Slam attacks, any major bombing errors being investigated (presumably due to the cost of the weapons).
- video encodings still in process -