The Automatic Computing Engine (ACE) was a British early electronic serial stored-program computer design by Alan Turing. Turing completed the ambitious design in late 1945, having had experience in the years prior with the secret Collossus computer at Bletchley Park. The ACE was not built, but a smaller version, the Pilot ACE, was constructed at the National Physical Laboratory and became operational in 1950. A larger implementation of the ACE design was the MOSAIC computer which became operational in 1955. ACE also led to the Bendix G-15 and other computers. Background The project was managed by John R. Womersley, superintendent of the Mathematics Division of the National Physical Laboratory (NPL). The use of the word Engine was in homage to Charles Babbage and his Difference Engine and Analytical Engine. Turing's technical design Proposed Electronic Calculator was the product of his theoretical work in 1936 "On Computable Numbers" and his wartime experience at Bletchley Park where the Colossus computers had been successful in breaking German military codes. In his 1936 paper, Turing described his idea as a "universal computing machine", but it is now known as the Universal Turing machine. Turing was sought by Womersley to work in the NPL on the ACE project; he accepted and began work on 1 October 1945 and by the end of the year he completed his outline of his 'Proposed electronic calculator', which was the first reasonably complete design of a stored-program computer and, apart from being on a much larger scale than the final working machine, anticipated the final realisation in most important respects. However, because of the strict and long-lasting secrecy around the Bletchley Park work, he was prohibited (because of the Official Secrets Act) from explaining that he knew that his ideas could be implemented in an electronic device. The better-known EDVAC design presented in the First Draft of a Report on the EDVAC (dated 30 June 1945), by John von Neumann, who knew of Turing's theoretical work, received much publicity, despite its incomplete nature and questionable lack of attribution of the sources of some of the ideas. Turing's report on the ACE was written in late 1945 and included detailed logical circuit diagrams and a cost estimate of £11,200. He felt that speed and size of memory were crucial and he proposed a high-speed memory of what would today be called 25 kilobytes, accessed at a speed of 1 MHz;