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Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine

The machine, a forerunner to Alan Turing's Bombe, played a crucial role in Allied victory of WWII.

Cambridge University Engineering alumnus Hal Evans has built a working replica of a 1930s electromechanical cryptologic device, one of the first-ever computers, and a forerunner for Alan Turing's famed Bombe, which helped the Allied forces to decrypt German Enigma ciphertext during WWII.

The machine built by Evans, a replica of a Polish cyclometer, currently resides in King's College, Cambridge. It was built in an effort to gain new insight into the history of the earliest computers.

RELATED: INTERESTING FACTS ABOUT THE MAN WHO BROKE THE ENIGMA — ALAN TURING

A machine crucial to Allied WWII victory

Evans began working on his hardware-based replica back in 2018 as part of his fourth year Master's project. The aim of the project was to gain a better understanding of cryptologist Marian Rejewski's cyclometer.

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Source: Hal Evans / Department of Engineering / Cambridge University

The cyclometer — a clear inspiration for Alan Turing's machine, the Bombe — was, for all intents and purposes, extinct. According to Evans, to his knowledge, his replica is the first fully-functioning hardware-based electromechanical cyclometer to exist since before WWII.

Historians believe that all of the original machines were destroyed in Poland in 1939 to prevent them from falling into the hands of German invaders.

"Due to the cost and the mechanical complexity of reproducing the original machine, other efforts to create a replica have been software-based to date," Evans explained in a Cambridge University press release.

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Source: Hal Evans / Department of Engineering / Cambridge University

"This presented an opportunity to recreate an important fragment of history. It has been a privilege to work on such a unique project which is a fascinating combination of Engineering, History, and Mathematics. The replica took just over a year to complete, with generous funding from King's College, which saw the obvious link with the work of one of its most famous alumni, Alan Turing," Evans continued.

Polish influence on Alan Turing's 'Bombe'

While Alan Turing's successes are celebrated in the UK — the dark history of Turing's treatment following WWII notwithstanding — less is known about the Polish contribution to cracking Germany's Enigma code.

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Marian Rejewski (left) and Alan Turing (right), two figures who played a vital role in cracking Germany's Enigma code, Source: 12

Researching into Rejewski and his colleagues, Evans explains how remarkably advanced the Poles were in their understanding of Enigma code compared to the British in 1939.

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Source: Hal Evans / Department of Engineering / Cambridge University

The Poles were, in fact, the first to solve the Enigma code. As Evans explains, they did so before the Second World War even started, using complicated high-level mathematical methods and specially-built machines.

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Source: Hal Evans / Department of Engineering / Cambridge University

"Their work and knowledge proved invaluable, and laid the foundations for the Allies' later success at Bletchley Park," Evans explained.

What did the cyclometer actually do?

Rejewski's cyclometer was built to crack the German Enigma code, which was created using Enigma machines — devices that still sell for incredibly high prices today for their historical value.

To perform its function, the cyclometer's builders semi-automated the process for calculating what was known as 'characteristics'  for every possible Enigma rotor starting position.

There were more than 100,000 of these rotor starting positions, and each of their characteristics had to be arduously calculated and cataloged in a card index system. The cyclometer was built in order to eliminate the need to calculate these characteristics by hand.

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Source: Hal Evans / Department of Engineering / Cambridge University

When in use, a specific number of the cyclometer's 26 lamps would illuminate, indicating the lengths of the characteristics of the Enigma code that was being deciphered.

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Source: Hal Evans / Department of Engineering / Cambridge University

Ultimately, using a replica Enigma machine, which historians know were available to the Polish cryptographers, would have taken 60 times longer. Using the cyclometer, Rejewski made the cracking of Germany's Enigma code a feasible operation.

Building and designing the cyclometer replica

Though Evans' replica of the original 1930s cyclometer was built to be as authentic as possible, the Cambridge University alumnus had to rely on limited surviving historical information.

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Source: Hal Evans / Department of Engineering / Cambridge University

“While there were some inevitable compromises in manufacturing a machine conceived over eight decades ago, we put considerable emphasis on using genuine parts and materials that would be faithful to the original machine," Evans explained. 

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Source: Hal Evans / Department of Engineering / Cambridge University

"This included using hard-wired Enigma rotors and reflectors (exact copies of the originals, consisting of Bakelite cores, spring-loaded brass pins, epoxy resin rings, and alloy finger wheels), silk-insulated wiring and waxed-linen cable lacing throughout, and Ebonite for the front panel, all of which would have been, or were documented to have been, used at the time."

Cambridge University Engineer Rebuilds Enigma Code-Breaking Machine
Source: Hal Evans / Department of Engineering / Cambridge University

"This included using hard-wired Enigma rotors and reflectors (exact copies of the originals, consisting of Bakelite cores, spring-loaded brass pins, epoxy resin rings, and alloy finger wheels), silk-insulated wiring and waxed-linen cable lacing throughout, and Ebonite for the front panel, all of which would have been, or were documented to have been, used at the time."

While it might not serve the same ultimate purpose as Rejewski's original machine, Evans' replica might help to decipher the history of one of the world's most fascinating precursors to the classical computer.

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