The National Museum of Computing is a UK-based museum that is dedicated to collecting and restoring historic computer systems, and is home to the world's largest collection of working historic computers. The museum is located on Bletchley Park in Milton Keynes, Buckinghamshire. It opened in 2007 in Block H – the first purpose-built computer centre in the world, having housed six of the ten Colossus computers that were in use at the end of World War II.
As well as first-generation computers including the original Harwell Dekatron computer—the world's oldest working digital computer— and mainframes of the 1950s, 60s and 70s, the Museum houses an extensive collection of personal computers and a classroom full of BBC Micros. It is available for corporate, group, school, and individual visitors. Although located on the Bletchley Park campus, The National Museum of Computing is an entirely separate registered charity with its own admission fee. It receives no public funding and relies on ticket sales and the generosity of donors and supporters. The museum has its own cafe and gift shop. In 2024 it was awarded full accreditation as a Nationally-styled museum by Arts Council England.
Origins The Bletchley Park estate was threatened with demolition and redevelopment in the late 1980s and early 1990s. It was saved in 1993 thanks to the efforts of the Bletchley Park Trust (BPT), which had been established in the previous year. One leading member – and secretary to the Trust – was a scientist with electronics and computer engineering skills named Tony Sale (1931–2011). He had worked for MI5 and later at the Science Museum alongside Doron Swade on a series of projects to restore some of the Science Museum's computer holdings to working order. Sale became the first curator of the Bletchley Park Museum, which in its early days was supplemented by more than a score of collections varying from WWII memorabilia to model railways. One of these centred around the history of computing and contained many historic computers, several of which were maintained in working order by enthusiastic volunteers, many of whom were members of the Computer Conservation Society. In 1993, Tony Sale and a group of volunteers started to rebuild a Colossus (a 'rebuild' as it contains parts from an original) in Block H. By June 1996 they had a prototype machine working, which was formally switched on by the Duke of Kent in the presence of Tommy Flowers who built the wartime Colossi. When in 2004 Block H came under threat of demolition, Sale and colleagues were able to protect it by obtaining Grade II listed building status for it. This led to the detachment of the computing collection from the Bletchley Park Trust museum, and the establishment in 2005 of the Codes and Ciphers Heritage Trust, which became the National Museum of Computing in 2007. Between 1994 and 2007 a group of volunteers led by John Harper built a working replica of a Turing-Welchman Bombe (used to help decipher Enigma–coded messages) in the BPT museum. This was relocated to Block H in 2018.
Exhibits The exhibits on display in the museum represent only a fraction of the collection, but are chosen to tell the story of computing developments in Britain. There are a number of galleries which can be visited in a broadly chronological sequence, starting with the working replicas of WWII machines that were developed and used by Bletchley Park codebreakers.
Bombe Gallery
This gallery tells the story of Cryptanalysis of the Enigma. Enigma machines were used by the Germans before and during WWII for sending secret messages. Alan Turing further developed, and Gordon Welchman enhanced, an idea implemented by Polish codebreakers, of a machine to assist in decrypting Enigma messages. This gallery houses a fully working replica of a Bombe machine, a working replica Enigma and various related artefacts. The replica Bombe was built by a team led by John Harper following the release in 1995 to the Bletchley Park Trust of some 2,000 BTM documents and drawings relating to the Bombes that they had built during the war. The replica is owned and managed by the Turing-Welchman Bombe Rebuild Trust, which provides and trains the volunteers who run and demonstrate the machine to visitors on a regular basis.
Tunny and Colossus Galleries
Separate from the Enigma story is the less well-known endeavour of the diagnosing and deciphering of messages produced by the more secure 12-rotor Lorenz SZ teleprinter cipher attachments, which is told in these two galleries. The Tunny galley exhibits one of the very few Lorenz SZ42 machines still in existence — something that nobody in the Allied side saw until after Nazi Field Marshal Albert Kesselring surrendered in May 1945, shortly before VE-day. 'Tunny' was the name given to the messages, to the unseen cipher machine and to the British-built emulator of it. The gallery contains a reproduction of part of the original Lorenz listening station at Knockholt in Kent, with its multiple RCA AR-88 radio receivers, pen recorders (undulators) and the sort of paper tape and teleprinter equipment that was used to record the messages and transmit them to Bletchley Park. Also on display is a working replica of a British Tunny machine that exactly emulated the Lorenz machine and a working replica of the Heath Robinson machine, the forerunner of Colossus.
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