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Enigmas of Bletchley Park

In January 1940, Bletchley Park made the first British wartime break into the German Enigma cipher – greatly helped by information passed on by Polish cryptographers. However, that first break was only the beginning. Enigma was not a single machine, but a family of machines. Developed for commercial use in 1924, Enigma was adopted by German armed forces from 1926. Its original design was adapted for the German military, secret service and state, and used by Germany’s allies. Each change posed a fresh challenge to the Codebreakers. These Enigma machines, held at Bletchley Park, represent some of the many types in use before and during WW2.

This Collections Uncovered album was first published on 27 March 2019.

Enigma D, A1214. The Enigma D was developed in 1926. It is the earliest model on display at Bletchley Park, but already more sophisticated than the original design. Its three rotors, which scrambled letters to create the encryption, could be removed and placed into the machine in any order. Its reflector, which directed the electrical signal in the machine back through the rotors, was also settable. This machine was delivered to the Italian Navy in 1932 and used by Benito Mussolini. It was captured in Northern Italy by US Naval Officers on 29th April 1945.

Enigma K, K289. The Enigma K was developed in 1927, just one year after the Enigma D, and had a very similar design. It could produce 1,782,206,400 possible encryptions. The letter ‘K’ comes from the German Kommerziell (commercial), and many were purchased by German users – such as the railway. This machine was one of a batch sent from Germany for use by Nationalist forces during the Spanish Civil War (1936-1939) and was used at the military headquarters in the Canary Islands. An anti-glare panel is stored inside the lid, to shield the lampboard in strong light.

Enigma I, A02192. From 1927, a plugboard was added to the front of machines used by German armed forces. This was the Enigma I, the most common version in use during WW2. Far more complex than the Enigma K, Enigma I machines could produce 103,325,660,891,587,134,000,000 possible encryptions.

Enigma I plugboard. The Enigma I was the first model to use a plugboard, a feature exclusive to German military machines. It had 26 sockets marked with the letters of the alphabet and connected by double-ended cables. This had the effect of swapping pairs of letters after a key was pressed but before the signal reached the rotors. Standard German procedure dictated that 10 cables were used. This multiplied the permutations produced by the rotors by 150,738,274,900,000, adding significant cryptologic strength to the Enigma.

Enigma I, A16992. Captured Enigma machines were brought to Bletchley Park for research. This example was heavily modified by the Codebreakers. The plugs have been removed and a small plugboard added to the left side of the case. This appears to have altered the wiring of the reflector, possibly to test the effect of changing reflector wiring on the machine’s encryption.

Enigma I, A16992. Enigma I machines had three rotors, plus a fixed reflector. The rotors could be placed in the machine in any order and, in 1938, an additional two rotors were issued to give the operator a choice of five. The wiring inside the rotors could also be offset, by moving the outer ring of each rotor. Each different combination of settings for these parts gave a different encryption.

Enigma M4, M5846. On 1 February 1942 the German Navy started using a four-rotor Enigma machine, the Enigma M4. The Bletchley Park Codebreakers were locked out; the techniques and procedures they had designed to tackle three-rotor Enigma needed to be updated. Enigma M4 used three moving rotors, chosen from a possible eight, plus an additional non-moving rotor, chosen from a possible two, as well as a plugboard. These improvements gave 60,176,864,903,260,346,841,600,000 possible encryptions. It took 9 months for the Codebreakers to break into Enigma M4 traffic, known as ‘Shark’, giving access to vital Atlantic U-boat communications.

Enigma T, T244. The Enigma T was developed in 1942 for communications between Germany and Japan. It was based on the commercially available Enigma K; the Germans did not wish to supply another power, even an ally, with their military Enigma. Uniquely, the wiring of the entry disc which connects the keyboard to the rotors was scrambled. Although it had no plugboard, its encryption was strengthened by additional notches on its rotors. Each notch triggered a ‘turnover’ in the next rotor along, stepping that rotor ahead by one letter. Whereas most models had one notch per rotor, the Enigma T had five, resulting in a highly irregular pattern of movement. The traffic it generated, named JN-18 at Bletchley Park, was rarely intercepted and so difficult to break.

Enigma G, G312. The Enigma G was developed in 1931 and designed to be smaller and more portable than other models. This machine belonged to the Abwehr, the German military intelligence service. It was part of the sub-family of ‘Zählwerk’ Enigmas, which utilised cog-wheels rather than the usual levers and pawls to move the rotors. This meant that they could be ‘stepped back’ to correct mistakes, and, uniquely, the reflector moved during encipherment. The Enigma G used a high number of turnover positions to produce a complex rotor movement, leading to its nickname at Bletchley Park, the ’11-15-17 machine’.

Enigma G, G110. This example is a rare type of Enigma G. Part of a shipment delivered to the Hungarian armed forces in 1931, it is one of two surviving machines with a printer connection.

Enigmas of Bletchley Park

This Collections Uncovered album was first published on 27 March 2019.

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