Further reading

There are any number of books available about Ultra. Three that I found good as background to how it was done are listed below. All of these have a lot to say about U-boat ciphers but much less about Luftwaffe ones. Once the Luftwaffe traffic was broken into it was read consistently, access to the naval traffic was much more precarious and that makes for a dramatic narrative.

Hugh Sebag-Montefiore Enigma: The Battle for the Code (Phoenix, 2001) ISBN-10: 0753811308 ISBN-13: 978-0753811306

Montefiore goes from the invention of the Enigma machine through pre-war espionage to early Polish successes and into the wartime work of Bletchley Park.

F.H. Hinsley & Alan Stripp (Editors) Codebreakers: The Inside Story of Bletchley Park (Oxford Paperbacks, 1994) ISBN-10: 019285304X, ISBN-13: 978-0192853042

Very technical at times, this is the one to read if you want a step-by-step guide to setting up and using an Enigma machine. You could almost build one with the information given here.

David Kahn Seizing the Enigma: The Race to Break the German U-boat Codes, 1939–43 (Arrow, 1996) ISBN: 0099784114) Arrow Books Ltd, 1996.

Purely naval, as the title says but a reminder that subterfuge and sheer audacity played a vital part alongside mathematical genius.

The website Tony Sale's Codes and Ciphers is an excellent reference source on the work of Bletchley Park.

Most importantly, the files themselves: I understand that DEFE3 material is available on microfilm in Canada and the USA but all my research in this area has been done at The National Archives in Kew, London. You might like to start by looking at their online catalogue.

And I thoroughly recommend a visit to Bletchley Park itself, the museum is fascinating.