Seventy Years Ago This Month at Bletchley Park

January 1940

The War. 

With no land fighting, except in Finland where the Finns are resisting the Russian invader, the war has become fought primarily at sea. There is a little air activity. On 8 January in Britain rationing is extended (it already covers meat) to reduce imports of sugar and flour.

Hitler postpones the offensive against the West. 

It is known from reports by officers working for Admiral Canaris who controls the Abwehr, the German counter-intelligence service, that Hitler is planning an attack. His Air Force needs eight days of consecutive good weather to destroy the French Air Force.  Continuing bad weather causes Hitler to postpone several times the attack set for 17th January. It is to be a drive to the Dutch and Belgium coasts to secure a base for further operations. But on 12th January a German light aircraft crashes in Belgium with the plans for the airborne element of this attack. On 15th January, Belgium refuses the British request for passage of troops across their country.  On 16th January Hitler, knowing that the Allies have these plans, decides to call the offensive off until the spring since the consecutive days of clear weather his Air Force needs cannot be counted on at this time of year.

The War in Finland.

 In terrible weather conditions, on 22nd December the Finns had counter-attacked at Suomussalmi and driven the Russians back across the frontier by the end of the month.  The Finns employ local encirclement operations and pinpoint attacks on small but key targets. Some aid and volunteers from the West are now at last reaching Finland.  The ability of ‘little Finland’ to withstand the assault by the Russian masses helps to strengthen the view that the Russian army is in a pretty poor state, a belief held in both Germany and the UK.  The Russians are forced to adopt different tactics based on extensive bombing of road and rail communications until they are ready to mount a renewed massive offensive on 12th February 1940.  One impact of the fighting in Finland is that both the Allies and the Axis planners focus attention on Scandinavia.  Hitler wishes to acquire bases in Norway to protect his iron-ore supplies coming by coastal waters from the north of Sweden. He orders preparations to be made for an invasion of Norway, for 21st February 1940.

Liaison with the Poles and French.

The First Wartime Break into Enigma. Following their escape as the Germans overrun their country in September, the Polish code-breakers had been established working with the French in the Château de Vignolles at Gretz-Armainvillers, 30 kms to the east of Paris. This Intelligence Centre is run by the newly promoted Colonel Gustav Bertrand who had been the liaison officer from the French Intelligence Service to the Polish codebreakers for some years past.  Because they have lost most of their documents and equipment it took some time before the Poles could get back into effective work.  They have been unable to return to breaking the German Enigma traffic in the way they had been doing before 15th December 1938, when the Germans increased from 3 to 5 the choice of wheels for the three slots in the machine.  But liaison with the British at BP is good and a secure teleprinter link has been established.  The British have undertaken to produce the Zygalski sheets, for what is known as the “Netz” method of breaking Enigma.  John Jeffreys has carried this out, assisted by Pat Hempsted, working under Dilly Knox and alongside Alan Turing and others in Cottage 3.  John has used a specially developed machine, the ‘Mouse’, in Hut 1, to help determine where to punch the holes in these sheets, a total of over 2 million holes being required in a complete set of sheets. Dilly Knox had had to fight off the impatience of the top management of BP while this machine was being developed. The first set of sheets was completed before Christmas. Nigel de Grey records that the completion of the first 2 million holes was celebrated “with ceremony and conviviality” in Hut 1. 

It is known that the second copy of 24 sets out of the 60 required (one set for each of the possible 60 wheel orders, each set consisting of 26 sheets) was ready for dispatch to France with a note dated the 28th December. It is probable that the British Military Intelligence liaison officer to the Château de Vignolles team, Captain K. MacFarlan took them out when he returned from Christmas leave on 4th January.  The complete second set was ready by 7th January but these were taken out by Alan Turing when he was going to see them on 17th January.  (He was going out to discuss the problem of the turn-over position of the two new wheels, where the information GC&CS had received had been incorrect, though whether this error had been introduced by the Poles or the British is not clear). The Poles broke an Enigma key that day using the sheets, in the presence of Alan Turing.  It was the German Army administrative key (“Green” as named by BP) for the 28th October 1939.   Of course there is normally little to be gained in terms of Intelligence information from breaking such an old key. It is said that the break was made with the first wheel-order checked. Probably Alan had shown them a way of reducing the wheel-orders that had to be tried. French interception stations were able to pick up certain transmission that the British Y stations could not hear, so a message that looked promising, perhaps by the use of a ‘cillie’, could be selected.  And of course any break is useful to the code-breakers as it helps them to understand the features of that particular key.  In this case it showed that the Germans had not introduced further modifications to their Enigma machine or procedures on the outbreak of war.  But had they introduced changes on the 1st January 1940? (The methodical Germans tended to introduce security changes on the first of the month).

The First Break into Enigma at BP. 

Alan Turing returned to the UK with the corrections to the wheel-turnover errors, and on about 22ndJanuary the Research Team made BP’s first break into Enigma, being the Green of the 25th October 1939 using the same Netz sheet method.  Two others breaks were made within a couple of days, probably the Red for 17th January 1940, and then the Red for 6th January.  The Germans had not modified the Enigma machine or their procedures, so BP is in serious Enigma business at last!  Of course for German Air/Army Enigma (but not for Naval Enigma that used a more secure method of indicating the message start settings) reading a key enabled all the other messages intercepted in that key setting to be decrypted just as a German cypher clerk would do it, typically for one day until the key settings changed at mid-night. Moreover, the Netz work was reduced as methods were developed for decreasing the number of wheel orders that had to be tried, based on the way the German cypher clerks sometimes chose transparently insecure message start code-wheel positions and indicators.  Studying the way the Germans select their indicators has probably occupied a significant amount of the time of Dilly Knox and his Research team.  It is known that the Poles much admired this work, which they called the ‘Knox method’, as it often reduced the number of Zygalski sheets that had to be stacked.  Despite the great news of the break into Enigma, for security reasons an immediate blackout was imposed so that few people in BP or Whitehall knew what had been achieved. [In the next three months some 50 settings were to be solved, though generally with considerable delay.  On some days, in addition to the Green (German Army administration) they broke the Blue (Air Force practise) and the Red (Air Force general operational & administrative communications, sometimes called the Air Force to Army liaison key). Because the war was static at the time, the Intelligence information obtained was not of much value, but the potential for when the war went mobile was now clear! And indeed, though the Germans achieved total surprise in their invasion of Norway on 8th April, BP broke the German campaign key, the Yellow, on the 15th April. Thereafter they broke the Yellow almost every day and often currently until it lapsed at the end of the Norwegian campaign in the middle of May 1940.   That this success with Enigma had little, if any, direct impact on the conduct of the fighting in Norway, nor indeed in any major way on the conduct of the war for many months to come, until procedures were developed for handling this priceless information, is one of the tragedies of the Intelligence war].

Attack on Enigma by the “Bombe” method.

Alan Turing, 26, is working on the design of his “bombe” machine for finding the Enigma key settings.  Alan does not rely on the approaches that the Poles had used, and which John Jeffreys was using, believing that the Germans would soon abandon the repeat sending of the code wheel settings. [In this he was proved right for they abandoned that repeat on 1st May 1940 except for the Yellow key].  Instead Alan relies on the “crib” approach where the code-breaker “guesses” what part of the message might say. The development for manufacture of the prototype “bombe”, a complex electro-mechanical machine, is in progress under “Doc” Harold Keen, the research director of the British Tabulating Machine Co at Letchworth.

The Opening of the Enigma Handling Huts 6 and 3. 

Gordon Welchman, 33, has convinced the Deputy Director, Commander Edward Travis, that a large scaling up of the effort will be needed at BP when these methods produce results. Gordon subsequently said that this was his biggest contribution to winning the war. For, remarkably, Travis has persuaded Whitehall to provide the resources to back this gamble by funding the complex bombe machines and staffing up BP to handle the anticipated output.  All this expenditure had been committed at a time when BP had not broken a single German Enigma message! At a meeting that was held at BP on 5th December 1939, it had been decided to establish a separate team from the Research Section for the exploitation of the anticipated break into Enigma. This led to the building up in January 1940 of a “production” team for Enigma. The Enigma Army & Air Force Cryptography work was now based in Hut 6 and, shortly after the first break, Enigma Army/Air Force Intelligence work was established in Hut 3.  F. L. Lucas records ‘On a snowy January morning of 1940, in a small bleak wooden room with nothing but a table and three chairs, the first bundle of Enigma decodes appeared. The four of us who then constituted ‘Hut3’ has no idea what they were about to disclose’.  This Hut was on what is now the Mansion car-park, close to the tennis courts; they moved to what is now called Hut 3 in a few months time as the team grew; the original Hut 3 was renamed Hut 9, and became the Administration hut. At first it seems that responsibility for the team in Hut 6 was still nominally vested in Dilly Knox, even though he was much better suited to research than production work.  Edward Travis took direct responsibility for the Enigma work, with an office in Hut 8 as well as the room he held in the Mansion as Deputy Director.  John Jeffreys looked after the Sheet-stacking Room where the keys were found, and the Machine Room where the plain text of the intercepted messages was recovered by stripping out the cypher once that key for the day was known. Gordon Welchman took charge of the rest, and was made responsible for the whole Hut before many weeks had passed.  In total some 30 people were employed in Hut 6 in the early months. [They could hardly have imagined in these early days of the Hut’s life that the number of staff in Hut 6 would grow to some 570 before the end of the war!].

The Nomenclature of the Huts.

Following the practice in World War I (i.e. Room 40 in the Admiralty), for security reasons the Enigma teams were named and always referred to for the first Hut in which they were housed. The huts were built and occupied roughly in numerical order, with the first four available during the last months of 1939.  When a team moved into other accommodation, usually into the brick Blocks, for security and administrative convenience reasons the teams retained their Hut title; the original Hut building would then be renamed, usually by adding 10 to its initial number. 

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