Tony Sale, who has died aged 80, was responsible for rebuilding the second wordl war Colossus code-breaking computer and for launching a successful campaign to preserve the Bletchley Park cryptography centre for the nation. The operation at Bletchley, Buckinghamshire, shortened the second world war by many months, but for almost three decades its existence was one of Britain's best kept secrets. When the war was over, the 10 Colossi – considered by many to be the world's first electronic computers – were broken up and the people who had built and worked with them were sworn to secrecy for ever.
It was only in the early 1970s that the persistent efforts of Brian Randell, a computer scientist at Newcastle University, led to the government formally admitting to the existence of the code-breaking operation and releasing a set of eight photographs of the Colossus. It was on the basis of these that in 1993 Sale embarked on the most challenging technical project of his life. Over 14 years, he and a team of volunteers built a working replica of the 2,500-valve Colossus.
Sale showed an early talent for engineering and tinkering. At the age of 12, using Meccano, he built a primitive robot, the first of several. In 1950, at the age of 19, he demonstrated a lifesize robot built from parts of a Wellington bomber fuselage. "George" was radio-controlled and could shuffle along on feet powered by castors. The robot generated huge popular interest and featured in newspapers and cinema newsreels. Last year, George was brought out of his 60-year retirement and again captured much media interest.
Sale was educated at Dulwich college, south London, where he obtained his "highers" in the sciences and history. There was no money for university, so he enlisted in the RAF for his national service. He became an instructor in radar at RAF Debden, near Saffron Walden, Essex, and attained the rank of flying officer. On his return to civilian life in 1952 he became a research assistant at Marconi's Great Baddow Research Laboratories, Chelmsford.
There he worked for another engineer, Peter Wright – later of Spycatcher fame. In 1954 Wright was recruited by MI5 as one of its first scientists, specialising in radio interception. Sale joined him in 1957 at the height of the cold war. The two of them equipped a van with radio detection equipment which enabled them to locate clandestine Russian communications stations in London. Sale left MI5 in 1963 with the rank of principal scientific officer, and for the next five years led a team on weapons design for the defence contractor Hunter Engineering in Ampthill, Bedfordshire (now a subsidiary of Lockheed Martin).
In 1968 the software industry was beginning to take off in the UK, and Sale formed one of the first firms, Alpha Systems. The company survived for more than 10 years – a good track record in this volatile new industry. He went on to found two further software companies before becoming an independent consultant in 1986. Sale was an active member of the British Computer Society. He founded its Bedfordshire branch and in 1986 was hired to co-ordinate a study group on the future of the society, under the then president Sir John Fairclough.
In 1989 he was hired by the Science Museum, in South Kensington, as a senior curator. There, together with Doron Swade (later assistant director of the museum), he led a series of projects to restore some of the museum's computer holdings to working order – rather in the spirit that railway curators restore ancient locomotives. At the same time he established the Computer Conservation Society, a joint venture between the museum and the British Computer Society. The society is dedicated to preserving computer history and restoring hardware and software. It has become a model for similar heritage ventures around the world.
In 1991 Sale learned that Bletchley Park, which after the war had become a Post Office training establishment but was now owned by BT, was under threat of redevelopment. With a group of like-minded colleagues, he started a campaign to save it for the nation. It took some years to mobilise powerful support – including that of the then prime minister, John Major – but eventually a charitable trust was formed. Private benefactions and a Heritage Lottery Fund award turned it into a major museum and tourist attraction.
Sale decided that the centrepiece of the Bletchley Park museum should be a working replica of the Colossus. To everyone except Sale, this looked impossible, since there was little more to go on than the set of photographs. Undaunted, Sale renewed the top-level security clearance he had enjoyed at MI5 and went about interviewing the surviving engineers who had built the Colossus – now mostly in their 80s. They had good memories, and one even had a project notebook, but there was still a lot of guesswork involved.
In 1995, however, there was a breakthrough. Under its Freedom of Information Act, the US government had released a shoal of classified wartime documents including a detailed technical description of the Colossus, written by a visiting US army scientist. This transformed the project from imagineering to engineering. Whereas Sale and his wife, Margaret, had personally funded the project in the beginning, sponsors now began to come forward. With the help of volunteers, and the donation of wartime valves from hundreds of electronic hobbyists, the Colossus was completed in 2007 and placed in the National Museum of Computing at Bletchley Park.
Sale's achievements in building Colossus and leading the campaign to preserve Bletchley Park were widely admired. He gave hundreds of lectures describing the project and was a script adviser to numerous documentary series, as well as the 2001 film Enigma, based on the Robert Harris novel. Among his honours were two honorary doctorates and the silver medal of the Royal Scottish Society of Arts in 2000. He remained a fixture at Bletchley Park up to his last days.
Sale is survived by Margaret, herself a Bletchley Park stalwart, three children and seven grandchildren.
• Anthony Edgar Sale, computer scientist, inventor and museologist, born 30 January 1931; died 29 August 2011
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