Seventy Years Ago This Month at Bletchley Park

July 1939

The Germans Prepare for War.

The behaviour of the German government since Hitler came to power in 1933 has left little doubt that he is planning more aggression in Europe. Germany had started the expansion of its armed forces in 1934, and repudiated the Versailles treaty in 1935. They then marched into the Rhineland in 1936. There were many in both the UK and France who wanted to believe that this was all a reasonable reaction to a grossly unfair Versailles peace treaty after the Great War of 1914 –1918. And the argument that a strong Germany would act as a bulwark against the ‘Bolshevik hordes’ of Russia was widely canvassed. But perhaps above all, the politicians as well as their public simply could not face the thought of another war after the horrors of the, then recent, past. This changed abruptly when the Germans launched the Anschluss by marching into Austria in March 1938. By then their persecution of the Jews was clear for all to see. When Hitler made it known that he was about to occupy Czechoslovakia the British Prime Minister, Neville Chamberlain, flew to Munich in September 1938, and came back waving that infamous bit of paper which seemed to promise “peace in our time”. The German occupation of the Sudetenland followed in October, and the British public felt a sense of guilt that we had bought a temporary peace at the expense of our friends in the East. Few now doubted that war was inevitable. Rearmament was now pushed forward rapidly, though the British armed forces had been so run down that there was much work to be done, so the postponement was welcome before what was seen as an almost inevitable conflict.

In March 1939 the Germans occupied the rump of Czechoslovakia, and by July 1939 it had became clear that their next target was to be Poland. Hitler resented the loss of direct access to East Prussia because of the creation, under the Versailles treaty, of the Polish Corridor to Danzig (Gdansk) on the Baltic. In March 1939 he told his Army staff that Poland was to be the next target, and set 1st September as the date for the attack. The integrity of Poland was guaranteed by France by a treaty dating back to 1921, and was reinforced by Britain in March 1939. But the abrogation, in April 1939, of the German-Polish non-aggression treaty, and the German discussions with the Russians about a pact, made it inevitable that Poland would soon be at war. Poland began urgent military preparations during July. [They had mobilised one million men by the time the Germans attacked with five armies totalling one and a half million men on 1st September 1939].

24/25 July 1939: The Meeting with the Poles at Pyry.

In 1930 the Polish General Staff’s cypher bureau in Warsaw recruited three young mathematicians, Marian Rejewski, Jerzy Różycki, and Henryk Zygalski, from a cryptology course at Poznan University. By 1933 they had managed to work out the wiring of the Enigma machine in use by the German services, and to break some keys, having achieved the first break over Christmas 1932. They received some help from a German spy, Hans-Thilo Schmidt, under the control of the French, in particular Captain Gustav Bertrand, said to have been head of the French radio Intelligence work. But despite this help, the Polish success was a remarkable feat. They were able to read German army and some air force keys regularly right up until the beginning of 1939, despite the changes introduced by the Germans, though not the naval cyphers after German procedure changes introduced in May 1937. However, in December 1938 the Germans added two more code wheels to the three in use with most of their military Enigma machines, providing a choice, from the now five wheels available, to fill the three slots in the Enigma machine at any one time. This increased the possible wheel start positions by a factor of ten, which prevented the Polish cryptographers from breaking all but a few keys in 1939. They did manage to work out the new wheel wirings because the German counter-Intelligence Service (the Abwehr) inexplicably continued to use the old procedures until 1st July 1939, seven months after the other Armed Services had made the changes. Thereafter the Poles were unable to break more than the occasional key, which was exceptionally sad for them, for now they needed the Intelligence the breaks would give them more than they ever had before, at a time when the Germans were massing on their frontiers.

On 24/25 July 1939 at the invitation of the Poles, the British and French cryptographers went to meet them at their site near Mokotov-Pyry in the Kabackie Woods, a few miles south of Warsaw. There, the Poles handed over their working models of the German Enigma machine, and gave full details of the wiring of the machine and the 5 code-wheels. They explained their methods, including the use of the Zygalski sheets, and showed them their machine, the Polish ‘Bomba’, that they employed for finding the key settings using the encoded, but twice repeated, wheel start positions sent by the Germans at the beginning of their messages. The team from the British cryptography centre, that worked under the name Government Code & Cypher School, GC&CS, included the ageing but still brilliant code-breaker Dillwyn Knox and Alastair Denniston who was soon to become Director of Bletchley Park. (The third member of the British party was apparently introduced as a Professor Sandwich of Oxford University. It was probably Lord Sandwith, Head of DNI 9 dealing with naval Y stations, who may have been representing the head of the British Secret Intelligence Services. He seems to have taken no part in the technical meetings. Years later, Marian Rejewski remembered that Captain Bertrand showed at the meeting that he knew Sandwich well). This meeting gave the British the confidence of knowing that breaking the German Service Enigma on a systematic scale could be done, and shortened the time before Bletchley Park could first read Enigma messages by giving them the internal wiring of the machine and its code-wheels. (Dilly Knox had broken an Italian Enigma key at least once, a year or so before, but that machine did not employ the ‘stecker board’ feature of the German Service machines).

Acquisition of Bletchley Park by GC&CS.

In May 1938 Bletchley Park had been acquired to provide a war-time home for the Government Code & Cypher School. This body nominally reported to the Foreign Office, but was a tri-service operation. It had been created in 1919 by the merger of the cryptography teams from the Army and Navy. It acted under instructions from the Joint Intelligence Committee of the Chiefs of Staff but with direct relations with the three Service Ministries as well as the Foreign Office. By 1939 it was clear that the German armed forces, as well as other bodies such as their railways, were using closely related cyphers based on the Enigma machine, so the case for retaining a single body to attack the enemy cyphers was strong. It was decided in the spring of 1938 to move GC&CS from London to Bletchley Park on the outbreak of war, to become the so-called ‘War Station’.

Captain Ridley’s Shooting Party.

From the day of acquisition in May 1938, Post Office engineers had been at work laying cables to connect Bletchley Park with the Ministries in Whitehall, via the main cable connecting London with the north of the country which ran through near-by Fenny Stratford. Then, in August 1938, “Captain Ridley’s shooting party” descended on the Park for the duration of the Munich crisis. Captain Ridley was a naval officer in MI6 who was in charge of the logistical operation of the move, and his ‘hunting party’ was the cover name to explain the arrival of this rather strange looking group of people. (The cover name suggests it was about 12th August that they moved in). After the Munich crisis was over they returned to London.
The Admiralty declared that the dress rehearsal move had not worked well, as part of its unsuccessful campaign to recall the naval contingent to direct Admiralty control. [The full move to Bletchley Park started on 1st August for the Military Service Sections and on the 15th August 1939 for the Diplomatic & Commercial Sections].

The Building of the first Huts

was probably ordered as a result of the overcrowding in the Mansion at the time of the Munich crisis. Hut 4, which became the Naval Section Hut, was immediately alongside the Mansion, with Hut 5 the Military Section Hut close behind it. It is said that at least one of the several huts that would be built on what is now the Mansion car-park was in existence by the autumn of 1938, with the others of the first bunch of five certainly in existence by the end of 1939. Presumably the building, or occupation, of the Huts followed in numerical order – as went on throughout the war. As a security measure, teams were known by their initial Hut number, even after they had moved elsewhere.

A Radio Listening Post
for the Foreign Office, M.I.6, was established in the water tower of the Mansion, with a great rhombic array aerial strung out round some of the huge Wellingtonia trees not far beyond what is now the car-park, manned by a team provided by the Royal Signals. The name ‘Station X’ stems from this installation, perhaps because it was the 10th station of its type. The associated radio transmitters occupied the first of the Huts, where Hut 1 stands to this day by the tennis courts. It would have been in operation before July 1939, though the whole listening post was soon to be dismantled and sent to Old Whaddon Hall, some six miles from Bletchley Park, because of the security risk it represented. [A brick annex was to be added to Hut 1 in late 1942].

British Cryptography in World War I.

During the First World War, the Royal Navy had a thriving code-breaking team, which grew to employ about 100 staff based around what became known as Room 40 in the Admiralty. It was led by Sir Alfred Ewing, who had been the Admiralty’s Director of Naval Education, and became the Vice-Chancellor of Edinburgh University in 1917. Thereafter the head of Room 40 was Captain Reginald Hall, always known as ‘Blinker’ Hall. One of Ewing’s first recruits in 1914 was Alastair Denniston, a language teacher from the Royal Naval College, who became the working head cryptographer of the Room 40 team. After the First World War Denniston became the first Director of GC&CS and remained in that post until February 1942. Ewing also recruited several academics from Cambridge, such as Nigel de Grey who became Deputy Director of GC&CS, Dillwyn Knox and Frank Birch who all three went on to play distinguished roles at Bletchley Park during WWII. It is said that Room 40 gained ‘complete mastery of German naval cryptographic methods’, and the Intelligence gathered proved very valuable, especially in 1917, though the failure of the Admiralty to develop proper procedures for distributing the Intelligence caused several lost opportunities. Their successes led the German navy to adopt radio silence during its major fleet operations during 1918. During the war it was said to have produced a total of about 15,000 decrypts. Perhaps the most famous of the exploits of the Room 40 team was from work on diplomatic cyphers, the decryption and skilful use of the ‘Zimmermann telegram’ which played its part in bringing the USA into the war in 1917. Both Nigel de Grey and Dilly Knox played a major part in the work on this telegram. The War Office had no centralised cryptography unit, though it did have a small team under Brigadier Anderson who worked on German military cyphers. They were much helped by the French, who broke the German military code used on the Western front early in 1914, and remained the leading practitioners of military Signals Intelligence throughout that war. After 1914, radio intercepts declined as static warfare developed so landlines took much of the military communications, though there was some revival in 1918. There were several Signals Intelligence teams in the field, who seem to have worked more by ‘traffic analysis’ than by decryption. Much of the Signals Intelligence obtained in the field stemmed from physical tapping of forward telephone cables, carrying plain language traffic. By the end of World War I, the War Office central team was led by Major Malcolm V. Hay, and consisted of 34 military officers, 11 civilians & 40 ladies.

GC&CS between the Wars.

In 1919 it was decided to bring together the cryptography activities of the Government into a single organisation, ambiguously called the Government Code & Cypher School. At first it was operated under the Admiralty but in 1922 it was transferred to work under the Foreign Office, along with the other Intelligence activities, such as spying. The F.O. continues to act as the parent body for British Signals Intelligence activities to this day. The public function of GC&CS was the security of British official communications, a role that the Director at BP continued to have responsibility for throughout WWII, though the actual work was carried out during the war from Mansfield College, Oxford in order to be close to the Oxford University Press who printed the key sheets, etc, for them. The formal Director of GC&CS was the head of the Secret Intelligence Service, but in practice the Director was his Deputy, Alastair Denniston, who continued in that role at BP until February 1942 when he was transferred back to run the Diplomatic and Commercial Sections of GC&CS when they returned from BP to the offices that they had occupied since 1925 in the Broadway Buildings in London (opposite St, James Park). For much of the inter-war period the staff of GC&CS was about 50 of whom about 30 were support clerical staff. The Munich crisis in the autumn of 1938 led to GC&CS expanding rapidly, reaching some 180 total by the time of the evacuation to Bletchley Park (BP). The main task of GC&CS between the wars was deciphering diplomatic codes and cyphers, paying increasing attention to the Service cyphers of Germany and Italy as the war approached.

The Bletchley Park Trust welcomes the preparation of these notes, but the authors are responsible for
the statements and the views expressed.