This is one of 10 x 1st stamps in the A-Z of the UK set issued in 2012.

Station X Bletchley Park Station X, a radio intercept station, is located in Bletchley Park, an estate located in the town of Bletchley, in Buckinghamshire, where during World War II, 12,000 people worked in total secrecy. It was the site of the United Kingdom's main decryption establishment, the Government Code and Cypher School (GC&CS), where cphers and codes of several Axis countries were decrypted, most importantly the ciphers generated by the German Enigma and Lorenz machines. The high-level intelligence produced at Bletchley Park codenamed Ultra, provided crucial assistance to the Allied war effort. Sir Harry Hinsley, a Bletchley veteran and the official historian of British Intelligence in World War II, said that Ultra shortened the war by two to four years and that the outcome of the war would have been uncertain without it.

Block C, a building at Bletchley Park used to break the Enigma Code, which contributed to the allied victory in the Second World War, has been given Grade II listed status. Post Office engineers played a vital part in the code breaking activity at Bletchley Park during the war, from maintaining vital communications such as teleprinters to building code breaking devices, including work on Colossus computers, the world’s first programmable computer, for which we can thank Tommy Flowers, the Post Office engineer for his vital work. So secret was the work that after the war Churchill ordered the computers to be dismantled and destroyed. Alan Turing devised a number of techniques for breaking German ciphers, including the method of the bombe, an electromechanical machine that could find settings for the Enigma machine. The bombe was featured in the February Britons of Distinction issue, to mark Turing’s centenary.

Modern Card by Bletchley Park Trust.
Stamp: 1st class, Station X Bletchley Park, Milton Keynes.
Postmark: Station X Bletchley Park 10 Apr 12 .