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Posted in Short read , Written by Dr Tacye Phillipson, Senior Curator of Science

This model of Enigma machine was the most famous device used by the German Navy to encode and decode military messages during World War 2. At the time, it was considered a very complex device, and the code it produced, unbreakable.

A colour photograph of a 4-rotor enigma machine in a wooden box and another smaller wooden box with 5 extra rotor wheels. The machine is black and has a number of keys on the top front and many jack sockets at the front edge with number and wires attached to some — A 4-rotor Enigma machine with a box of spare rotors. Museum reference T.1994.63.

This particular machine was made in 1944 and uses four code rotors and is housed in a wooden case. It is a rare example as it has with it a smaller case containing five interchangeable spare rotors. This machine is the most advanced Enigma machine, used by the German Navy in World War 2; those used by other military forces only had three rotors, and two spares.

Similar machines were first made in the early 20th century, and the first ‘Enigma’ was invented by German engineer Arthur Scherbius in 1918, who sought to sell it for commercial rather than military purposes. During the following years, the Enigma was redesigned and improved several times.

A colour photograph of a close-up of the 4 rotor enigma machine showing the front which has Manu jack sockets on the front side with numbers and wires attached to some and a keyboard on the top. There is a separate box with extra rotor dials which are metal and circular. — A close up of the 4 rotor Enigma machine and extra rotors. Museum reference T.1994.63.

How Enigma machines worked

The machine is an electro-mechanical cipher device that relies on a series of ‘rotors’ to convert plain text messages into scrambled coded text. What made the code system very secure was that messages were sent out using a different daily password and other settings, that were taken from a secret key list. In order to decrypt a message, the receiver would need to know that day's settings from that key list.

This short video demonstrates how a Swiss Enigma machine translates messages into cipher, and how this can then be deciphered.

Cracking the code

The Enigma code was eventually cracked by British Intelligence officers working at Bletchley Park, near London, and is thought to have significantly helped to bring the war to a swifter end.

The aim was to work out the daily settings and allow the messages to be read. The machines devised in the decoding work were called Bombes, developed using existing methods designed by Polish mathematicians.

The fact that messages could be deciphered had to be kept a closely guarded secret to prevent the Germans changing any encryption methods. Information received from deciphered material was codenamed 'Ultra'. Ultra secrets were the highest form of classification, even more valuable than information classified ‘Most secret’.

Decades of secrecy delayed the recognition of the work carried out at Bletchley Park, which is now a museum commemorating those top secret activities.

The Enigma encoding machine is on display in the Communicate gallery at the National Museum of Scotland.