[6] One leading member – and secretary to the Trust – was a scientist with electronics and computer engineering skills named Tony Sale (1931–2011).

[7] 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.

[8] 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.

[9] 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.

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.

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.

Alan Turing further developed, and Gordon Welchman enhanced, an idea implemented by Polish codebreakers, of a machine to assist in decrypting Enigma messages.

[12] 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.

[13] 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.

At the heart of the machine is a set of five counters that, for each transit of the looped paper tape containing the message, count the number of times that defined Boolean expressions deliver a specified value.

[45] This concept of packet switching was first presented in public in the US at the inaugural ACM symposium in Gatlinburg, 1967, and in the UK at the IFIP Congress, 1968, in Edinburgh.

[47] ARPANET's first link was established between the University of California and Stanford Research Institute in November 1969, by which time the NPL's packet-switched network was already operational.

Fund-raising continues and donors have included Bletchley Park Capital Partners, Fujitsu, Google UK, CreateOnline, Ceravision, Insight software,[50] PGP Corporation, IBM, NPL, HP Labs, British Computer Society (BCS), Black Marble, and the School of Computer Science at the University of Hertfordshire.

[52] The Museum is normally open to the public 4 days a week: Tuesdays, Thursdays, Saturdays, and Sundays, from 10:30am to 4:30pm during the winter period, extending to 5pm during the summer months.