Virtual Bletchley Park
by Tony Sale

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Tony Sale's
Codes and Ciphers

The pre-history and early history of Bletchley Park
Many of the early organisation problems in Bletchley Park during WW II arose from the pre-war relationships between the various agencies involved.

To understand these relationships it is necessary to trace their evolution from their roots in and before WW I and the changing circumstances in the inter war period.

In 1909 a government committee had recommended the formation of a Security Service Bureaux (SSB). It was to have two sections, a foreign section which became the Security Intelligence Service (SIS) headed by Commander (later Captain Sir) Mansfield Cumming (1859-1923), all subsequent Directors were known as "C" in his honour, and a home section which eventually became MI5. The first head of the home section was Vernon Kell.

The Director of Naval Intelligence in WW I had been Admiral William 'Blinker' Hall who had set up Room 40. Also recruited to Room 40 was Sir Alfred Ewing. There ensued a tussle for control of Room 40. Ewing lost and resigned in October 1916. But Ewing had recruited for Room 40 people who were to become key players at Bletchley Park in WW II, namely Denniston, Knox, Birch, Clarke and de Gray.

Naval Intelligence emerged from WW I covered in glory as a result of the success of Room 40. Army Intelligence had much less success and Air Intelligence had not started.

After WW I there was clearly a need for a codes and ciphers organisation independent from the services and after some deliberations the Government Codes and Ciphers School (GC&CS) was formed in 1919. However it was not part of SIS but came under the Admiralty of which Admiral Sinclair was director of Naval Intelligence (DNI). The first head of GC&CS was Denniston.

By 1922 most of the work in GC&CS was on diplomatic codes and control of GC&CS moved from the Admiralty to the Foreign Office.

Then in 1923 Cumming died and Admiral Sinclair was appointed head of SIS with Menzies as his deputy. SIS was by then also funded through the Foreign Office. GC&CS now came under Admiral Sinclair.

The Navy, the Army and later the Air Force, all had their own Intelligence Directorates. These forces Directorates also had sections within SIS, the Army from 1923, the Navy from 1924, and the Air Force from 1930. These SIS sections were there to collect and collate SIS agents reports and information from other SIS sources. But the forces also established service sections within GC&CS to enable service personnel to be trained in codes and ciphers.

In 1925 GC&CS moved to Broadway but although now in the same building as SIS, still there was no direct contact between the two organisations.

Prior to WW II all these various sections were semi-autonomous and not communicating. GC&CS was not supposed to produce intelligence, just decrypts as and when required and to offer expertise in code breaking. It was supposed to pass on its code breaking expertise to the forces intelligence directorates so that they could perform interception, decryption and intelligence. The problem was that in the inter war years there was very little interception from foreign forces but there was diplomatic traffic. Thus the Naval and Army Directorates and GC&CS found themselves dealing with mostly diplomatic traffic.

This began to change with Italy's invasion of Abbasynia in 1935 and the first appearance of the German use of Enigma.

By the beginning of 1938 the situation was:

Naval Intelligence Directorate (NID) headed by Rear Admiral J A G Troup SIS Naval Section headed by Fredrick Russel GC&CS Naval Section headed by William Clarke

Military Intelligence Directorate (MID) headed by SIS Military Section headed by GC&CS Military Section headed by John Tiltman

Air Intelligence Directorate (AID) headed by SIS Air Section headed by Fred Winterbotham GC&CS Air Section headed by Josh Cooper

SIS headed by Admiral Sinclair, Deputy Menzies GC&CS headed by Alistair Denniston reporting to Menzies and Sinclair

After the purchase of Bletchley Park in early 1938 by Admiral Sinclair, the Service Sections of GC&CS went to the Park in September 1938 to test its suitability for occupation if war came. The occupation was co-ordinated by Captain Ridley.

This was partially successful. It showed the need for better communications and more accommodation space than just the Mansion.

This first occupation was withdrawn in October 1938 and everyone returned to Broadway.

In early 1939 the construction started of wooden huts clustered around the Mansion. The first huts built were numbered 1,2,3,4 & 5. A Telephone Exchange was built outside the Billiard Room.

On 1st August 1939 SIS and GC&CS moved to Bletchley Park, "the war station". SIS occupied the first floor of the Mansion with GC&CS occupying the ground floor.

The Naval Section moved quickly into Hut 4 alongside the Mansion on the south side. The Army Section moved first into Sir Herbert Leon's dining room. When Hut 5 was completed the Army section moved there and the dining room became a mess room. The Air section moved into the drawing room on the right of the entrance and Denniston occupied the room on the left.

Knox, Jeffreys and Turing moved into the Cottage in the Stable Yard.

Dilly Knox and Denniston had brought back from the meeting with the Poles in the Pyry Forest, on the 25th July 1939, the wheel wirings of the German Enigma machine and the ideas for the Zygalski Sheets, the Netz, and of Rejewski's Bomba. John Jeffreys set up, in the Cottage, a production line for Netz, now known as Jeffreys Sheets. By December 1939 complete sets were prepared. One copy was taken to France to the Chateau Vignolle, where the Polish code breakers had arrived from Poland. Dilly Knox and Alan Turing first tried the Jeffreys Sheets on some unbroken 1938 traffic. When this worked they were ready to try current traffic. The French and Poles at Vignolles also tried on current traffic and early in January 1940 they succeeded. The first keys broken were for the Red, German Air Force Enigma messages.


This page was originally created by the late Tony Sale
the original curator of the Bletchley Park Museum