The Codebreakers - Enigma, Bletchley Park & The Battle Of The Atlantic

Monday 6 October 2008, 18:15  

Dr Mark Baldwin MA MSc PhD


Dr Mark Baldwin’s talk had been eagerly awaited by many and some 120 people gathered at the Metropole Hotel on the evening of the 22nd for the presentation. It’s difficult to know what to put in and what to leave out when summarising a presentation as detailed and informative as this one, so for those who were unable to attend the following hopefully gives a flavour of the evening.

A brief history

The presentation began with a brief history of the Enigma machine. After the end of World War One it was accepted that wireless was fundamental to communications. The disadvantage with wireless was that it was insecure; there was no way of preventing someone other than the intended recipient from listening to the transmission. Therefore, anything secret has to be encrypted before transmission.

The Enigma machine has its origins in an encryption device developed by Dutch naval officers during World War One. The idea, using rotors to encrypt one character to another, was copied by a German employee of the Dutch company that was producing the machine at the time. (It had not been patented because the officers and their employer, the Dutch navy, had been unable to agree who owned the patent).

A company was set up in Berlin to produce the machine and sell it for commercial, rather than military, use to enable companies to encrypt commercially sensitive information before sending it to its intended destination. A few machines were sold but the company was not prosperous.

Adoption by the German military

The machine was adopted by the German military, who added a system of wiring and plug-boards to increase the number of encryption possibilities. In its final form the machine had more encryption possibilities than there are atoms in the observable universe.

The German military placed great faith in the Enigma system, believing it to be entirely secure. It was not, however, secure against mathematics. In the early 1930s, three Polish mathematicians tried to break the code, and by 1932 had managed to reverse engineer the wiring in an Enigma machine, which theoretically meant they could decipher encrypted transmissions.

Dr Baldwin went on to explain how the Enigma machine worked, using schematic and cut-away diagrams of parts of an Enigma machine to illustrate this. The machine could be reconfigured using the plug board, or by substituting different rotors, in order to change the encryption.

By performing this reconfiguration on a regular basis, messages sent would be encrypted differently. Therefore anyone who had broken one particular set of codes would not be able to decipher messages sent after the Enigma machine had been reconfigured.

The German military was divided up into between 20 and 30 different networks. Every month, each network was given instructions on how to set up the machine to encrypt and decrypt messages.

Initially the various sections of the German armed forces all used machines with three rotors, but later on the Navy adopted the use of machines with four rotors. Some networks were issued with as many as eight different rotors, and part of the set-up procedure involved selecting which rotors would be inserted in the machine.

The Enigma machine was not a transmitting or receiving device. Nor did it record the output of encryption in printed form. An outgoing message would be written down and given to someone tasked with encryption, who would encrypt the message using the Enigma machine character by character and write down the message in its encrypted form.

Once an outgoing message had been encrypted, it would then be transmitted using traditional radio communications. The recipient would need to write the received message down, then decrypt the message character by character using their Enigma machine to reconstruct the original message.

The work of Bletchley Park

Dr Baldwin then gave an account of the work done at Bletchley Park, illustrated by numerous photos of the inside and outside of the various buildings including the famous Hut Six and also the Bombe, which was not a computer as is sometimes believed but rather an electromechanical device which assisted in decryption by simulating different rotor positions of an Enigma machine and applying a certain test; this eliminated a large number of possible combinations and left a much smaller number of possibilities that were examined by hand. It is said that the work of the Bletchley code breakers shortened the war by as much as two years.

Dr Baldwin highlighted the poor state of repair of some of the buildings at Bletchley and the difficulty faced in securing funding for maintenance of the site, which is regrettable given its importance in the history of the Second World War (since the presentation took place, it has been announced that English Heritage have awarded a grant of some £330,000 to Bletchley Park to help with the cost of these repairs).


The presentation ended with a lively question and answer session, and an opportunity for those present to try using an Enigma machine for themselves. The applause at the end showed how much Dr Baldwin had engaged the attention of his audience throughout, and we are very grateful to him for a most enjoyable and informative evening.