Virtual Wartime Bletchley Park
by Tony Sale

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Tony Sale's
Codes and Ciphers

Gordon Welchman: Getting BP organised.

Once they had started breaking Enigma in the Cottage, using Jeffreys sheets, Welchman, who had quite independently thought of the sheet method, realised that a massive break into the German Enigma traffic could be achieved.

This arose from the German key system for Enigma. The Enigma settings were changed every day at midnight, so for 24 hours everyone on a particular communications net were on the same Enigma settings. Thus, Welchman realised, if just one Enigma message could be broken and the base settings found, all the traffic for that whole 24 hour period could just be decrypted.

Welchman thus saw that a rapid increase in manpower would be required at Bletchley Park and that the organisational structures had to be put in place immediately to handle the intelligence material. He put together a paper on his proposed structure and took it the Deputy Director, Commander Travis. Travis immediately saw the importance of it and gave it his enthusiastic backing. In a very short time it was being implemented. Welchman said later that this was probably his greatest contribution to the War effort.

Welchman's Organisation Proposal

The Welchman proposal was for the following organization which remained basically unchanged throughout the War.

Army/Air Force Code breaking Hut 6.

Army/Air Force Intelligence Hut 3.

Naval Code breaking Hut 8.

Naval Intelligence Hut 4.

and the Hut numbers became the cover for these activities.

The Bletchley Park Intelligence Machine


Y Stations

The Code breaking Huts, 6 & 8
The Intelligence analysis Huts 3 & 4
Within each code breaking hut there was a Registration Room.

An important part of the work of the Registration Room was Traffic analysis. Gordon Welchman had shown the importance of this activity. All incoming intercepts received from the Y Stations were meticulously logged and cross indexed to build up a detailed picture of the signals from all parts of the German Forces. This helped the Machine Room in locating cribs and possible "kisses". This was the Park name for a message sent twice on different Enigma key settings or once on Enigma and once using a different cipher which another department in the Park could break.


This page was originally created by the late Tony Sale
the original curator of the Bletchley Park Museum and is currently being hosted by Rich Sale Limited.