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These codes were eventually broken by the evolution of prototype programmable computers, developed in a new section at BP called 'Newmanry', which could help calculate the probable rotor positions used by Tunny, called 'Heath-Robinson' (first used in May 1943), and the Tunny Machine in October 1943, which enabled the ultimate development of the 'Collosus' computer, which is now regarded as the world's first programmable computer. This machine was created in December 1943 and was operational in February 1944 and included an optical character reader and a continuous punch-tape input. It was ingeniously created by using Post Office values and telephone exchange equipment. The Collossus Mark 2 was developed by June 1944 and the department was expanded into Block H. The machine was actually quite powerful as a simulation of the code breaking programme ran on a net-work of modern PCs is little faster.

The decoding of the codes with the aids of these computers meant that the volume and speed of the decodes increased considerably. The Enigma codes especially could be decoded as fast as 14 minutes (though on average within an hour), and could rapidly be in the field with the Allied Commanders. Tunny, was however much slower and decrypts took on average 4 days.

The volume of messages being decoded grew greatly over the war in spring 1943, 39,000 Enigma messages were decoded, however, by 1944-5, 90,000 per month were being decrypted. Again the volume of Tunny codes being cracked was much smaller, in June 1944, only 300 a month were being solved,. however, by October 1944, 1,200 each month were being deciphered and most could be solved in a day. Around D Day, approximately half of decoded messages were naval. There were also out-stations for Bletchley Park, at Wavendon House and at Stanmore.

At the end of the War the work at Bletchley Park remained entirely secret. Those leaving the service at BP were unable to refer to their actual war-service and most could only receive generalised references for their war service. Furthermore, many BP staff could not even reveal their knowledge of certain foreign languages they had learnt, in pursuance of work. Only those joining peace-time British Intelligence services could directly use their work.
The Enigma secret was finally revealed by the controversial publication of the Ultra Secret' by F W Winterbotham, in 1974, and a flow of publications and now films, since. Some former BP operatives, are still reluctant to reveal the full-extent of their war-time activities.

After the war, the owners of BP were British Telecom, and it was all nearly bulldozed for redevelopment in 1992. However, the Bletchley Park Trust was formed to save the site and the site, with the Mansion and some of the surviving war-time huts and block houses now form a fascinating place to visit, not least because the decoding story and the story of the computer, is amply told through the Mansion, the surviving war-buildings, displays and museums on site, along with the recreation of the Colossus computer on site.