Bletchley Park is a nineteenth-century mansion and estate near Milton Keynes in Buckinghamshire, constructed during the years following 1883 for the English financier and politician Sir Herbert Samuel Leon in the Victorian Gothic, Tudor, and Dutch Baroque styles, on the site of older buildings of the same name. It has received latter-day fame as the central site for British (and subsequently, Allied) codebreakers during World War II, although at the time of their operation this fact was a closely guarded secret. During the Second World War, the estate housed the British Government Code and Cypher School (GC&CS), which regularly penetrated the secret communications of the Axis Powers – most importantly the German Enigma and Lorenz ciphers; among its most notable early personnel the GC&CS team of codebreakers included Alan Turing, Gordon Welchman, Hugh Alexander and Stuart Milner-Barry.
According to the official historian of British Intelligence, the "Ultra" intelligence produced at Bletchley shortened the war by two to four years, and without it the outcome of the war would have been uncertain. The team at Bletchley Park devised automatic machinery to help with decryption, culminating in the development of Colossus, the world's first programmable digital electronic computer.Codebreaking operations at Bletchley Park came to an end in 1946 and all information about the wartime operations was classified until the mid 1970s. After the war, the Post Office took over the site and used it as a management school, but by 1990 the huts in which the codebreakers worked were being considered for demolition and redevelopment, and the Bletchley Park Trust formed in 1991 to save large portions of the site from developers. More recently, Bletchley Park has been open to the public and houses interpretive exhibits and rebuilt huts as they would have appeared during their wartime operations, as well as The National Museum of Computing, established on the site which includes a rebuilt Colossus machine, and receives hundreds of thousands of visitors annually.