Bombe Rebuild Project 

A faithful reconstruction of the machine that made breaking large numbers of Enigma messages possible on a regular basis. Click here for the Bombe Rebuild Project Website.   Below, Bombe Veteran Jean Valentine officially switches on the machine for the WRN'S Switch-On and Bombe Veteran Ruth Bourne receives Honourary Membership of the Bombe Rebuild Team from John Harper, leader of the Project Team - Enigma Reunion September 2007.  Also, HRH The Duke of Kent, alongside the Rebuild Team, officially switches on the Bombe Rebuild - July 2007.

Before World War II, Polish crypto-analysts had already designed an electro-mechanical machine to test Enigma rotor settings called a ‘Bomba’. However, in December 1938 the German military changed their system slightly thus thwarting the Poles’ ability to decrypt Enigma messages.

Before the war started, the Poles passed all of their information over to Britain and France and two mathematicians working at Bletchley Park, Alan Turing and Gordon Welchman, were able to build on this research to develop the ‘Bombe’ machine. Turing and Welchman exploited the fact that enciphered German messages often contained common words or phrases, such as general’s names or weather reports and so were able to guess short parts of the original message. These guesses were called ‘cribs’. The fact that on an Enigma machine no letter can be enciphered as itself made guessing a small part of the text even easier. It also meant that the potential number of settings that the Enigma could be in on that day was greatly reduced.

Before running the Bombe, the wiring at the back of the machine was connected in accordance with a ‘menu’ drawn up by the codebreakers based on cribs. The Bombe found potential Enigma settings not by proving a particular setting, but by disproving every incorrect one in turn.

Over 200 of the Bombes were built by the British Tabulating Machine company at Letchworth, all of which were destroyed after the war.