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