Naval, World War I, Pembroke and Scarborough
Military, Chatham 1921, Sarafand 1923,
Air, Waddigton 1927
FO, GC&CS, Denmark Hill 1923
Earliest evidence of inter-service liaison:
The Cryptographic and Interception Committee 1924
Standing Sub-Committee, Co-ord of WIT intercept 1928
Became the "Y" Committee, 1938
Chair, head of GC&CS,
members, NID 9, MI 1(b), (later MI 8), AI 1(e)
YC sub-committee, programme of intercept and D/F
The Intelligence Units of the Armed Forces.
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This first occupation was withdrawn in October 1938 and everyone returned to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.
Early Enigma breaks
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
The breaking of Enigma, in January 1940, immediately raised a large number of
problems, the prime one being how to keep secret the very fact of breaking Enigma.
The code breakers involved, and Denniston and "C", realised that it was only
because of German errors in the use of Enigma, that it had been broken. By
eliminating these errors and with just a few changes to the procedures for using
Enigma, the Germans could render breaking impossible. Thus it was absolutely vital
that the Germans never realised that Enigma was being broken. The results from
breaking Enigma had to be disguised so that even Allied recipients could not
discover that what they were receiving came from breaking Enigma.
The result was a complete isolation of the Enigma code breaking within Bletchley
Park and the immediate setting up of a small section to handle the translation,
emending and concealing of the Enigma decrypts before they left Bletchley Park. All
outputs were to go straight to Winterbotham at SIS Broadway and they were
concealed by being attributed to agents reports, just like the other outputs from SIS.
The first series had the prefix CX for agents reports and series /FJ.
The dilemma of this was that SIS agents reports were thoroughly discredited by the
service Intelligence organisations, so not much notice was taken of CX/FJ even
though because it was Enigma decrypts it was impeccably accurate.
The section for translating Enigma decrypts was first known as the FJ Section. It
was headed by Commander Saunders, a Naval Officer brought down from
Broadway because of his knowledge of German and his Intelligence background.
He was joined by a civilian, F J Lucas, an Army Captain Edgar and a Flt Lt from the
Air Force. They moved into the first Hut 3 which was a hut between Hut 2, the
recreation Hut and the Tennis Courts. They soon became known as "Hut 3" as a
cover for their work and this stuck for the rest of the war despite various moves to
bigger and bigger buildings.
Because the decrypted Enigma traffic was originating from the German Air Force
(GAF), Hut 3 was producing intelligence primarily for Air Force Intelligence. (AID). A
problem arose because there was already an Air Section within GC&CS headed by
Josh Cooper. Because of the need for secrecy about breaking Enigma, Josh
Cooper's section knew nothing about the output form Hut 3. The Air Section was
breaking German, Italian and other non-machine codes and ciphers.
Another difficulty was with interception. In 1939 most Naval interception was being
done at Flowerdown and Scarborough, long established Naval Intercept stations.
The Military used Chatham for interception. The Foreign Office mainly used a Police
listening station at Denmark Hill. The Air Force had a station at Waddington. But all
these stations were taking very little foreign forces traffic, they were mainly taking
diplomatic traffic which went to the Foreign Office.
The Military Intercept station at Chatham was the first one to take Enigma traffic.
Before the January 1940 break it was thought that this was German Army Enigma.
Because at this time there was very little Enigma traffic, Chatham continued taking it
even after it was found that it was actually GAF traffic. However the Air Force had
decided to build an intercept station at Chicksands. When Enigma traffic increased
vastly during the German invasion of Norway, the Army pressed for Enigma
intercepting to be transferred to Chicksands. GC&CS initially resisted this because
the operators at Chicksands were mostly untrained and not expert at Enigma traffic.
There were just not enough radio sets to take all the possible Enigma traffic and
GC&CS called on Denmark Hill to help.
After much pressure it was decided to build more intercept stations, the Army at
Beaumanor and the Air Force at Forest Moor and Knockholt. Later stations were
built in Scotland and in the West Country, in all about 20 stations were in operation
at the end of the war.
Enigma interception was unique in requiring absolute accuracy in the first few
groups of a message. Without this level of accuracy the early Netz method for
breaking messages would not work and the later Bombe attacks also required a
high degree of accuracy for the "cribs" to work.
Chatham had exceptionally good intercept operators who could consistently
produce the high levels of accuracy required for breaking Enigma. GC&CS were
thus very concerned at plans by MI8 to transfer Enigma intercept to the relatively
inexperienced operators at Chicksands.
Gordon Welchman, in particular, demanded that GC&CS should have control of
interception and some rather acrimonious correspondence ensued with Colonel
Butler, head of MI8.
Traffic Analysis (WTI)
Another consequence from isolating Enigma was with Traffic Analysis. TA was
called W/T I in some quarters and eventually became part of SIGINT.
A number of different groups sprang up, each tackling their own small part of TA for
their own ends. For GC&CS, Enigma breaking depended heavily on knowing which
parts of the German forces were communicating using Enigma. Right from the
beginning listing messages was a vital activity with very close co-operation with the
intercept stations. An Intercept Control section was established in Hut 6 very early
The War Office, in 1939, was virtually completely ignorant about the German
communication systems, the order of battle and where forces were. Colonel Butler
had long held the view that Traffic Analysis could provide valuable intelligence. A
section was set up at 3 Cork Street in London to study the German communications
system. They hoped that by studying the Chatham activity reports they would be
able to make deductions about German intentions and order of battle.
Nearby in Broadway Buildings an independent section, organised by Cpt
Bolitho with the blessing of MI8, was endeavouring to break down the German
callsign system using tabulating machinery.
Lt Col Stratton started the "Central Intelligence Section" in the
Spring of 1940, at Caxton St in London for "The collation of
identities and locations from decodes with callsign research
and D/F plots to produce diagrams of German wireless layout".
In Autumn 1940 this was divided into Long Term Research
under Stratton and Short Term Research, known as the "Central Party",
based at The Warren, Harpenden.
Special Liaison Party
Cpt Lithgow, June 1940, Special Liaison Party
(SLP) at GC&CS in Hut 3 to study callsigns and
Not expected by GC&CS to be of any value, but
soon proved very useful indeed to Hut 6 and
VI Intelligence School was started in March 1941, to
concentrate on research into German methods. Most of VI IS moved
to Beaumanor in July 41 and SLP, now on staff of VI IS remained at
Eventually VI IS all moved to GC&CS in May 1942.
The CIS contribution became vital to the Hut 6 Enigma breaking efforts
and SLP helped Hut 3.
Both CIS and SLP fused into one in Feb 44 in G Block in Bletchley Park
and renamed SIXTA.
In August 1940, Godfrey, DNI, proposed that Naval "Y" should be
expanded to enable all German, Italian, French, Spanish, Russian
and Japanese Naval traffic to be read. He advocated removal of
departmental barriers so that all information from whatever source
should be pooled.
Did not have much effect.
Cryptanalysis and W/T Intelligence.
Sub-committee on relations between cryptanalysis
and W/T met July 41
Submissions sent in from Navy, Army and Air
Conclusion: Cryptography and WTI are not
mutually exclusive subjects but are inter-related
throughout the process of extracting
intelligence from interception and form one
There is no basis for comparison, no clash of
interests and there can be no apportionment of
effort between the two.
In September 1942 Colonel Sayer produced a paper on "Interception,
W/TI, Cryptography and Production of Intelligence",
This re-iterated the findings of July 1941.
Finally Commander Travis in July 43 proposed, based on Sayer's paper,
as an integrated whole:
"Who"? - Who sent it and to whom?
"Where"? - Where are they?
"What"? - What does it say?
The previous mistakes:-
(1) "What" is held to be cryptography while
"Who" and "Where" are held to be TA or W/T I
(2) "Who" and "Where" are treated as
intelligence sources independent of "What"
All should be embraced under SIGINT
This page was originally created by the late Tony Sale the
original curator of the Bletchley Park Museum