Lot 140
A 2 inch aluminium sphere of the type used in the Teddington ship tanks during the development of the Golf Mine "bouncing bomb". Discovered in a box of Sir Barnes Wallis' lectures slides on the "Dam Busters" raid, the spheres were the next evolutionary step after the garden marbles leading eventually to the development of the Highball and Upkeep bombs. Between 9 June and 10 September 1942, Wallis made use of one of the two large indoor water tanks of The National Physical Laboratory at Teddington on at least 18 occasions, he stated "I moored a wax model of a battleship several hundred feet up the tank, broadside on. We fired 2in diameter balls at it, when of course after hitting the freeboard of the ship, the sinking velocity of the ball combined with back-spin to move it towards the ship, and by adjusting the mean density of the ball we were able to pass it right underneath "the soft underbelly", to quote Winston Churchill.  £10000-15000