Seventy Years Ago This Month at Bletchley Park

December 1939

The War in the Air and at Sea.

With no land fighting, except in Finland where the Finns are resisting the Russian invader, the war is being fought primarily at sea.  There is a little air activity with an ineffective British air-raid on 18th December on the German fleet at Wilhelmshaven.  This raid demonstrated that the Air Ministry belief that their fast but lightly armed bombers were a match for the German defences was far from the truth. German radar had detected the bombers as they approached and their fighters shot down twelve of the twenty-two bombers. Following the mining of British coastal waters, on 28th November the British Government institutes a naval blockade aimed at preventing German exports.  Hitler announces that the defeat of the British is essential.  Once the German Army has defeated the French and the British on land, the primary task of the German Navy and Air Force would be to cripple the British economy.  This was to be achieved by a naval blockade, mining of the sea approaches, and aerial attack on industrial centres and ports.  German mine-laying activities and air reconnaissance flights are stepped up.  When asked by the British War Cabinet what this activity portends, the Joint Intelligence Committee replies that they can still only guess.

The Sinking of the German pocket battleship Graf Spee. 

The new German pocket battleship Admiral Graf Spee had sailed into the Atlantic before the outbreak of war.  It had sunk nine merchant ships before being tracked down by three British cruisers, the Achilles, the Ajax, and the Exeter and is badly damaged in the Battle of the River Plate on 13th December.  She takes refuge in the port of Montevideo in neutral Uruguay, but sails four days later, only to be scuttled before she comes out of neutral waters rather than face destruction at the hands of the waiting British ships.  Her captain commits suicide.  This victory was achieved without any help from signals intelligence, but by the skill of Commodore Harwood who correctly guesses where the pocket-battleship will be heading.  The Captain of the Graf Spee had been fooled into believing that a greater British force awaited him outside the port than had yet assembled there. This is the first British victory of the war, and so is much celebrated by the British population who are shortly to suffer tighter food rationing as supplies run short due to the shipping losses from mines & submarines.  The menace of the magnetic mines has been overcome with the deployment of the degaussing antidote, though Churchill decrees that damage by any type of mine is to be ascribed to magnetic mines, if at all feasible, to fool the Germans into believing that we have not found a solution.

Hitler prepares an 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 five days of consecutive good weather to destroy the French Air Force.  Continuing bad weather causes Hitler to postpone the date several times. Hitler sets 14th January as the date for the start of the offensive in the West. It is to be a drive to the Dutch and Belgian coasts to secure a base for further operations against the French and British.

Russia Invades Finland. 

On 30 November, in massive numbers, Russia had invaded Finland on an 800-mile front and bombed Helsinki, but to the world’s surprise the heroic Finns hold out. Russian tanks fail to make progress against Finish land mines and “Molotov cocktails” (improvised incendiary grenades).  Aid is promised Finland by the Western Allies, but it does not start to arrive until January. In terrible weather conditions on 22nd December the Finns counter-attack at Suomussalmi and drive 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. The Russians are forced to regroup and adopt different tactics based on extensive bombing of road and rail communications [until they are ready to mount a renewed massive offensive on 1st 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 on the 21st  February 1940.

Fighter Command is using Sigint sources to despatch fighter aircraft. 

The German Air Force is bombing and mine-laying, directed against the British Fleet and east coast shipping.  At this time there is no high-grade Signals Intelligence (Sigint) from Enigma traffic, for example. But interception of low-grade Sigint, such as German air-to-ground radio communications by the RAF intercept station at Cheadle, enables Fighter Command to husband its sparse resources.  Fighters can be despatched appropriately and shipping convoys can be warned of coming attack.  But these interceptions can throw no light on the German strategic plans.

At Bletchley Park the Air Section is busy attacking low-grade Sigint. 

Work is now well established at Bletchley Park on the various hand cyphers and minor codes that are being broken there at the time.  By now the Air Section, under Josh Cooper, has started to work a 24 hour watch, helped by four undergraduates from Cambridge, to speed up the decoding and translation work where this could not be done at the Y station at Cheadle. The team at BP is not helped by their lack of knowledge about the organisation of the German Air Force.  Nigel de Grey, who worked in Hut 3 and rose to be Deputy Director comments “It was probably felt, on the analogy of Hymns A. and M., that one step was enough for them at a time”.

Attack on Enigma by the “Netz” method.

In Cottage 3 in the Stable Yard the Enigma Research Section, under the nominal leadership of Dilly Knox, is working on the two methods that will lead to the break into Enigma to enable BP to acquire high-grade Sigint.  Dilly benefits from the knowledge that the Poles have broken Enigma, before the Germans introduced more code wheels, though Dilly probably told only a few of his colleagues what he had learnt from the Poles at the meeting near Warsaw in July.  John Jeffreys, from Downing College, Cambridge is working on their “Netz” sheet method, a way of rapidly finding certain combinations of the machine settings out of the many possible alternatives.  Because the Germans have increased the available choice of code wheels from 3 to 5, the method now requires ten times as many sheets as the Poles had been employing.  John, assisted by Pat Hempsted, finally completes the punching of the holes in the Netz sheets in mid-December in Hut 1, with the aid of an especially developed machine. Nigel de Grey records that when the 2 millionth hole is finally punched this is celebrated “with ceremony and conviviality”. But will the method work, or have the Germans introduced further changes?  The next few weeks will tell!

Attack on Enigma by the “Bombe” method.

Alan Turing, 27, fresh from Kings College, Cambridge where he holds a Research Fellowship, is working on the design of his “bombe” machine for finding the Enigma key settings.  Alan rejects 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 it on 1 May 1940]. It seems likely that the inexperienced Turing would certainly have discussed this with Dilly Knox and probably the others in the Cottage. Dilly Knox and his three brothers were accustomed to playing mental games with each other where it was a point-of-honour not to make it too easy for one’s opponent. So it may well have been Dilly who distrusted the Polish method of breaking Enigma because it relied on the Germans continuing to use a procedure that Dilly would have considered as providing an unnecessarily easy way of breaking their messages!  Instead Turing relies on the “crib” approach where the code-breaker “guesses” what part of the message might say. The 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.  During December, working at his digs one night, Alan deduces the method used by the German navy for transmitting Enigma indicator settings, making his first – but certainly not his last – great contribution to German naval Enigma decryption. It is a complex procedure involving two tables. These tables are changed every few months, so, though Alan works out how to recreate them once enough breaks are being achieved, breaking German Naval Enigma will always be a much more difficult and fragile process than breaking their Luftwaffe or even their Army Enigma, which employ a much simpler indicator method and so makes these signals much more vulnerable to code breakers.
Alan Turing subsequently recorded that it was on that very night in December 1939 when he had first worked out how the Germans carried out this procedure for transmitting the Enigma indicator settings that he had also first thought up the procedure, known as Banburismus. This would eventually enable the naval codebreakers in Hut 8 to reduce markedly the number of possible code-wheel orders that had to be tested on the ‘bombes’. It was a fiendishly difficult process to carry out, but while bombe time was scarce the adoption of the Banburismus procedure by the Naval Enigma team in Hut 8 made all the difference to their ability to break the German naval Enigma messages

Preparations to scale up the Effort. 

Gordon Welchman, 33, convinces the Deputy Director, Commander Edward Travis, 51, that a large scaling up of the effort will be needed at BP when these methods of breaking Enigma can be made to work. Remarkably, Travis persuades Whitehall to provide the resources to back this gamble by building the expensive and complex bombe machines and staffing up BP to handle the anticipated output. All this expenditure is committed at a time when BP has not broken a single Enigma message! At a meeting held at BP on 5th December, it is decided to establish a separate team from the research section for the exploitation of the anticipated break into Enigma. “Commander Travis had found younger men engaged on the Enigma problem with not only the knowledge required to grapple with the Bombe theory but men with an active sense of urgency”.  Following this decision, Alastair Denniston scribbles down a note ‘We are to fix an organisation for research and production. This being fixed no alteration is to be made by any members of the staff without reference to me’; then he thinks better of that and amends the last two words to read ‘…to Travis in the first instance or to me’. The Research Section would be led by Dilly Knox, and it is intended that the Production section should be led by Gordon Welchman, but Denniston cannot bring himself to tell the irascible Dilly Knox that this Production team will be formed by taking away staff from Dilly’s direct control. [Once Enigma was broken, this led rapidly to the establishment of the Enigma Production Section for Enigma work in Hut 6, Hut 8 and later Hut 3, “not independently of but separately from” the Enigma Research Section under Dilly Knox in the Cottage]. Meanwhile, the Polish codebreakers have escaped from Warsaw as the Germans approached, and are established with the French in the Château de Vignolles near Paris.

The Veteran Code-breaker, Dilly Knox. 

Dillwyn had been born in 1884, the son of a famous evangelical clergyman who by 1939 was the Bishop of Manchester. After Eton, Dilly entered King’s College, Cambridge, on a scholarship to read classics. After graduating he became a Fellow of King’s and started to make his name in the narrow but distinguished field of reading and translating ancient Greek papyri. This proved to be a first rate training for code-breaking, for he rapidly shone in that remarkable team that Sir Alfred Ewing put together during World War I in Room 40 in the Admiralty to read the German naval messages. Dilly made his name by breaking the German Admiral’s code, and contributed to the breaking of the ‘Zimmermann telegram’ that helped to bring the US into the war (along with the young Nigel de Grey).  After the war, though he never entirely broke his strong links to King’s College and work on papyri, to his friends’ surprise, he agreed to stay on in the new GC&CS for ‘work of national importance’, working under Alastair Denniston who had been the head cryptographer in Room 40. It is thought that it was Dilly who broke the Russian codes in about 1923, at a time when the British Government was desperate to know about the plans of the Soviet Comintern. In the 1930’s he turned his efforts to breaking Enigma, and in 1937 he succeeded in breaking a version of the machine used by the Italian navy, which was very similar to the widely used commercial version that lacked a stecker (plug) board.   He developed a way of facilitating the breaking of Enigma machines (without stecker-boards) using what he called rods; a way of representing the connections on the Enigma code-wheels in a slide-rule like device.  He made a major contribution to the attack on Enigma initiated in the Cottage in the first months of the war, before the ‘Production’ team broke away to handle German Luftwaffe, Army, and then Navy Enigma.  [Thereafter, Dilly built up a team of girls working with him in the Cottage. He concentrated on the Italian Naval Enigma, where their great work led directly to the British victory at Cape Matapan. He and his team then turned their attention to the German Abwehr Enigma, succeeding in breaking it before his death from cancer in February 1943].

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