The Enigma and the Bombe



The Mansion at Bletchley Park

The Mansion at Bletchley Park




This website describes how the German Enigma enciphering machine was broken by the British bombe - the cryptanalytical machine designed by Alan Turing and Gordon Welchman at Bletchley Park, the centre of Allied codebreaking during World War II.

The bombes were neither the only, nor the first, method of breaking the Enigma but the breaks facilitated by the bombes from 1940 onwards yielded intelligence in a quantity unprecedented in military history and made a major contribution to Allied victory.

The Enigma was not the only enciphering machine employed by Germany in World War II. The other machines, the Siemens T52 Geheimschreiber and the Lorenz SZ40/SZ42 Schlüsselzusatz were codenamed STURGEON and TUNNY respectively at Bletchley Park. The traffic derived from TUNNY was known at Bletchley Park as FISH. TUNNY was initially broken by hand methods due to an extraordinary German error and later with the assistance of Heath Robinson, an experimental punched paper tape comparator incorporating about 30 valves. Having shown the comparison method of cryptanalysis to be workable, a second, more practical machine, called Colossus, was designed to break the FISH machines. Colossus was arguably the world's first electronic computer and incorporated about 1600 valves.

The cornucopia of intelligence gleaned from the Enigma breaks and from FISH was known as ULTRA.

This page provides links to two essays, each with schematic diagrams. The first essay describes the Enigma enciphering machine and the second describes the logical operations of the British bombe. The Enigma machine, and its method of operation, is well-known and accordingly the essay concerning the Enigma is relatively concise. Since there is less material available concerning the logical operations of the bombe, this essay is of greater length and detail.

I have received a number of requests for the Enigma and bombe emulators which I wrote in Java. When time permits I intend to rewrite these as applets to enable them to run in Java-enabled browsers but as I am very busy this will take some time. I will also put essays on the Polish bomba, Heath-Robinson, Colossus and the FISH machines here in due course.

I am occasionally free to talk on the Enigma and the bombe. If you wish me to give a talk at your organisation please email me.

Click on the links below to go to the appropriate page.


Website Dedication

  1. In Memoriam: Lt Anthony Fasson and AB Colin Grazier
  2. How Fasson, Grazier and Brown's Action Enabled the Break into SHARK


The Enigma Machine - its construction, operation and complexity

  1. Brief Historical Background
  2. Description of the Enigma Machine
  3. How the Enigma was Set-Up and Operated
  4. Complexity of the Enigma


The Turing Bombe - what it was and how it worked

  1. Cribs and Menus
  2. Description of the Bombe
  3. How the Bombe was Plugged-Up
  4. How the Bombe Worked
  5. Checking the Stops in the Bombe
  6. The Sound of the Bombe


Naval Enigma


General Report on Tunny


Additional Material



Copyright © Graham Ellsbury 2003 - 2007.

It is unclear to me who owns the copyright of some of the photographs on this site. If I have breached your photographic copyright please email me and I will immediately remove the appropriate photograph or supply an acknowledgement, whichever you prefer.