Enigma – The Turing bombe rebuild project is being exhibited in Bletchley

An electro-mechanical device used by the British cryptologists to help decipher German Enigma-machine-encrypted secret messages during World War II.

The British bombe was developed from a device known as the “bomba”, which had been designed in Poland. The Poles were the first to break the military variant of the Enigma in 1932. At section BS-4 of Biuro Szyfrów (Polish Cipher Bureau), young Polish mathematician Marian Rejewski had recovered the wiring of the military Enigma machine. He was later joined by two further mathematicians, Henryk Zygalski and Jerzy Rózyki, who became involved in recovering the daily Enigma keys.

The Bombe sits in Block H, the home of the wartime Colossus machines. The original machine was destroyed after the war on the orders of Churchill / Image source

The initial design of the British bombe was produced in 1939 at the UK Government Code and Cypher School (GC&CS) at Bletchley Park by Alan Turing, with an important refinement devised in 1940 by Gordon Welchman.

The first machine, called ‘Victory’, was installed at Bletchley Park on 18 March 1940. A second Bombe, with Welchman’s diagonal board present, was installed on 8 August 1940. It was named ‘Agnus Dei’, later shortened to ‘Agnes’ or ‘Aggie’. The first machine (Victory) was later modified with a diagonal board as well.

During the course of the war, hundreds Turing-Welchman Bombes were built. To avoid the risk of losing them in case of a bomb attack, they were spread between Bletchley Park and its so-called Outstations in Wavendon, Adstock, Gayhurst, Eastcote and Stanmore, where they were operated by WRNS, RAF-technicians and civillian personnel.

This is the inside of the Turing Bombe, the part-electronic, part-mechanical code-breaking machine and forerunner of the modern computer, which cracked 3,000 messages a day sent on Nazi Enigma machines during the Second World War / Image: via commons.wikimedia.org

In 1994 a group led by John Harper of the BCS Computer Conservation Society started a project to build a working replica of a bombe. Recruiting volunteers, at one time numbering 60, the task of reconstructing the one-ton Bombe with its countless components and moving parts began. Although a few parts were sourced from the period, most were re-manufactured from the original drawings.

In September 1997, the reconstructed steel frame was installed in Hut 11, one of the original Bombe locations, and over the next five years the machine with its 12 miles of insulated wire was painstakingly assembled. In April 2002, the mechanical phase was completed.

In June 2003, the electrical phase began, then the manufacture of more than 200 drums and was commissioned in 2006/7. Bombe was officially unveiled in July 2007.

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