Tallboy or Bomb, Medium Capacity, 12,000 lb was an earthquake bomb developed by the British aeronautical engineer Barnes Wallis and used by the Royal Air Force (RAF) during the Second World War. At , it could be carried only by a modified model of the Avro Lancaster heavy bomber. It proved to be effective against large, fortified structures against which conventional bombing had proved ineffective. History Wallis presented his ideas for a 10-ton bomb in his 1941 paper "A Note on a Method of Attacking the Axis Powers", which showed that a very large bomb exploding deep underground next to a target would transmit the shock into the foundations of the target, particularly since shock waves are transmitted through the ground more strongly than through air. Wallis designed the "Victory Bomber" of , which would fly at at to carry the heavy bomb over , but the Air Ministry opposed a single-bomb aircraft, and the idea was not pursued after 1942. The design and production of Tallboy was undertaken without a contract on the initiative of the Ministry, following Wallis' 1942 paper "Spherical Bomb—Surface Torpedo" and the design of the "bouncing bomb" for the Dam Busters of Operation Chastise. The RAF therefore used bombs which they had not purchased and which therefore remained the property of Vickers the manufacturer. This situation was normalised once the weapon’s capabilities were established. Accomplishments of the Tallboy included 24 June 1944 Operation Crossbow attack on La Coupole which undermined the foundations of the V-2 assembly bunker and a Tallboy attack on the Saumur tunnel on 8–9 June 1944, when bombs passed straight through the hill and exploded inside the tunnel below the surface (stopping Panzer reinforcements reaching Normandy). The last of the Kriegsmarine's Bismarck-class battleships, the Tirpitz, was sunk by an air attack using Tallboys in Operation Catechism. Design Most large Allied, particularly British, Second World War aircraft bombs (blockbuster bombs) had very thin skins to maximize the weight of explosive that a bomber could carry. This was an improvement on the early part of the war when the explosive content of British bombs was low. To be able to penetrate the earth (or fortified targets) without breaking apart, the casing of the Tallboy had to be strong. Each was cast in one piece of high-tensile steel that would enable it to survive the impact before detonation. At the same time, to achieve the