Seventy Years Ago This Month at Bletchley Park

November 1939

The Phoney War Continues. The German and Russian conquest of Poland complete, there is no fighting on land. At sea the war builds up with our shipping losses mounting. Minor activity takes place in the air, with the first German bomber shot down over the UK.  But the overall atmosphere is one of waiting with mounting anxiety for the next blow to fall, with feverish preparations being improvised to meet a possible German attack.  In Poland the persecution of the intelligentsia and the Jews accelerates.

Hitler prepares an offensive against the West.  While secret peace negotiations were in progress, on 9th October Hitler had issued a directive to his commanders to prepare for an offensive through Holland, Belgium, Luxembourg and Northern France to take place on 12th November.  That date is known to the British Cabinet, due to a leak from officers working for Admiral Canaris who controls the Abwehr, the German counter-intelligence service. The British Intelligence survey at the outbreak of war had predicted that Germany would over-run Poland in three weeks and would then launch an offensive in the West during November. That the attack is imminent is confirmed by warnings from the Dutch Military Attaché in Berlin, via the Vatican. However, on 10th November Hitler orders a postponement because his army is not ready. 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. In a speech to his generals on 23rd November Hitler tells them that in the coming attack Britain would not have to be invaded because she “could be forced to her knees by the U-boat and the mine”. Reconnaissance flights and enemy mine-laying along the British coast intensifies towards the end of the month. When asked by the Cabinet what this activity portends, the Joint Intelligence Committee replies that they are in the dark and can only guess.

The Menace of the Magnetic Mines.  The German Battle cruiser Scharnhorst ventures out on 8th November and sinks the British armed merchant cruiser Rawalpindi with large loss of life. But the most serious problem at sea has emerged in the form of the German magnetic mines which have begun to wreak havoc on British and French merchant shipping. .  One scientific adviser in the Air Ministry does know about the German magnetic mines; for early in November Dr R. V. Jones had received from an unknown source the “Oslo” report. This document details the German advanced weapon research being carried out in a dozen fields, including magnetic mines and torpedoes, as well as the V weapons. Many in Whitehall believe it must be a plant, but Dr Jones becomes increasingly convinced of its authenticity and its great value as the new weapons emerge.  On 20th November a magnetic mine, dropped by air, falls on the mud flats at Shoeburyness.  It is dismantled and its secrets disclosed, enabling work on an antidote to commence.  The process of placing a “de-gaussing” electric cable round our ships is soon developed, and installation starts.  At that point it is discovered that another part of the British Admiralty had used magnetic mines in 1918 and ever since had been developing new versions, although it had been rather dilatory in getting them into production.

The Venlo Fiasco.  Two senior, but rather gullible, British Secret Intelligence Service officers in Holland walk into a German trap, believing that their German contacts represented a group of dissident German generals. On the authority of the Prime Minister who believes the contacts may be offering a chance for peace, and despite an explicit warning from the Naval Attaché at the Hague, they go to meet their contacts and are captured after venturing over the Dutch-German frontier on the 9th November. This helps the Germans to deepen the penetration of our agents in the Netherlands, which eventually leads to distrust by the British Secret Intelligence Service (MI 6) of the Dutch underground.  This had its disastrous consequences when the help of the underground was spurned at the time of the Arnhem venture, four long years later.

Russia Invades Finland.  On 30th November, in massive numbers Russia invades Finland on an 800 mile front, but to the world’s surprise the heroic Finns hold out aided by the national fury at the devastating Russian air raid on Helsinki.

At Bletchley Park, the Air Force Section breaks some German Air Force book codes.  The Air Force Section under Josh Cooper has been established in the room in the Mansion that had been the ante-room to the dining room for the Leon family who had been the previous owners. They are trying to tackle the encypherment by both the Germans and the Russians of their weather broadcasts, which started on the outbreak of the war.  And there are six “small codes”, book codes in use by the German Air Force for air-to-ground communication. They “had been solved as to system by Sq Ld Moore but were imperfectly reconstructed as to vocabulary” – in the words of Nigel de Grey who was then second-in-command of Air Section to Cooper. Professor F. E. Adcock, who had acted as a recruiter in Cambridge University, joined Moore in building up the code-books, while Miss R. M. Welsford decoded the day’s traffic. With the luck that so often favoured the hard pressed teams at BP, in mid-November a German bomber crashes in France carrying one of the six books.  This provides the complete vocabulary used in all these six codes up until May 1940.  However, this November the German Air Force introduces an additional batch of book codes.  Perhaps the most important item rescued from that crashed aircraft is the map chart revealing the German “Bomber Grid”, used to communicate positions.

At Bletchley Park work is in progress that will lead to the breaking of Enigma keys.  Work is now well established at Bletchley Park on the various hand cyphers and minor codes that are being broken there at this time.  But in Cottage 3 in the Stable Yard the Research Section, under the loose leadership of Arthur Dillwyn (Dilly) Knox, is working on the two methods that will lead to the break into Enigma. He benefits from the knowledge that the Poles have broken Enigma, before the Germans introduced more code wheels, though Dilly probably tells only a few of his immediate colleagues what he had learnt from the Poles at the meeting near Warsaw in July. Perhaps he told just Peter Twinn, John Jeffreys and Alan Turing – certainly not Gordon Welchman who, like Jeffreys and Turing, had joined the BP Research team from Cambridge when war broke out. John Jeffreys, fresh from Downing College, Cambridge, is working on the “Netz” sheet method, though it now requires ten times as many sheets as the Poles had been employing. Punching of the two million holes in the Netz sheets is in progress in Hut 1, with the aid of an especially developed machine.

Alan Turing, aged 27, fresh from Kings College, Cambridge, where he holds a Research Fellowship, is working on the design of his “bombe” machine. After an unpromising start he had begun to make his name, specialising in logical mathematics, for at Princeton in December 1936 Alan had given his first great paper, the title beginning with the famous words “On computable numbers…”.  In it he described a “thought experiment” imagining a machine that could add and subtract; John von Neumann called it a “Turing Machine” and it forms the basis of the theory of computation to this day. While in the USA, Alan experiments with a machine multiplier using relays.  On returning to Cambridge he was recruited to the shadow team who were ready to come to BP when the war broke out. He is a remarkable, but very shy man, who lacks the social graces.  Dilly Knox reports confidentially to the Director, Alastair Denniston, that Alan Turing is “very difficult to anchor down. He is very clever but quite irresponsible and throws out a mass of suggestions of all degrees of merit.  I have just, but only just, enough authority and ability to keep him and his ideas in some sort of order and discipline.  But he is very nice about it all”.  Dilly Knox encourages him to design a machine that could find the Enigma key settings.  Alan rejects the approaches that the Poles had used, and which John Jefferys was using for the Netz method, 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 1st May 1940].  Instead he relies on the “crib” approach where the code-breaker “guesses” what part of the message might say. Gearing up to manufacture  the resulting “bombe” is in progress at the BTM Co at Letchworth under Harold Keen, head of their Research team and always known there as ‘Doc’.
 
Preparations to scale up the Effort.  Gordon Welchman has convinced the Deputy Director, Edward Travis, that a large scaling up of the effort will be needed when these methods of breaking Enigma produce results. In September, he has sketched out what a room containing bombes and British-built Enigma machines might look like, and foresees that processes akin to mass production will be required. The current code-breaking procedures where the various tasks of decryption, translation, and writing the resulting out-going message are all performed, essentially, by one cryptographer could not continue at the volumes envisaged. This method would need to be replaced by a clear division of labour amongst a team of experts. Remarkably, Travis persuades Whitehall to back this gamble, even though not one German Enigma message has ever yet been broken in the UK either before or since the war began.

The Role of Edward Travis in the breaking of Enigma. Gordon Welchman was born in 1906, and so he was 25 years younger than his Director, Alastair Denniston, 22 years younger than his immediate boss, Dilly Knox, and 18 years younger than Edward Travis. Since Gordon did not get on well with Dilly, it maybe that he did not first discuss his ideas for scaling up the effort with Dilly, but it is interesting that he took them to Edward Travis rather than to Alastair Denniston to whom one might have expected Dilly to have reported directly. Alastair and Dilly had been together in Room 40 in the Admiralty during WWI, and had become close friends. From 1916 onwards, Edward worked on the security of Royal Navy cyphers, and on liaison on such matters with the Navy’s allies in France and Italy, and so probably had little contact with the codebreakers in Room 40.  They came together in 1919 in the newly formed GC&CS, with Alastair taking responsibility for cypher-breaking, and Edward for cypher security under him. This role-split seems to have continued in the early days at BP, though the cypher ‘Construction Section’ was now based in Oxford.  Travis had been made responsible for the Service Sections of GCHQ in 1938. It was not in Alastair’s character to spend much time out of his office visiting his staff, and in any case he was frantically busy coping with the administrative problems arising from the move to Bletchley and the subsequent expansion. But Edward Travis did make it a habit to get out, seeing the work on the ground and talking to the staff. So it seems that Travis was made responsible for the ‘Enigma’ Section, though Dilly often continued to write straight to Denniston. (Travis would have had a direct interest in the security of Enigma as at this time he was concerned with the deployment in the British Services of the TypeX machine, a machine designed on very similar lines).   On the 18th November Travis sent a minute to Denniston proposing that, once the first break has been achieved, the Enigma Section under Knox should be divided into two subsections, one dealing with ‘Research’ into the remaining Enigma problems such as Naval Enigma, and a ‘Production Section’ for the mass decryption of the Air & Army Enigma intercepts. He proposed that the Research Section should be run by Knox, the Production Section by Welchman.  It was just as well that it seems to have been Travis who fought the battle in Whitehall to get authority for the resources that would be needed for the expansion, since such battles were not ones that Alastair was good at, but were very much ones that Edward would prove to be a master at fighting and winning. Subsequently, Travis continued to take direct responsibility for the consequent Enigma huts, their staff, and the mechanisation programme.

The Rack Machine. Early in November Dilly Knox asks that a machine he calls the ‘Rack’ should be built for dealing with German naval traffic, where the repeated indicator was believed to be replaced by some form of look-up table. Once the first message a day had been broken using a ‘bombe’ machine, the decryption team would know which wheels and steckers were in place for the rest of that day, but it would still be difficult to break the subsequent messages without the look-up tables. The rack was to be a machine that would use the now known code-wheels and steckers to cycle through the possible message start positions, counting the number of occasions the letter ‘e’ was to be found in the message at each position of the code-wheels, to find the positions with the most. It was likely that one of these would be the correct start position. (The letter ‘e’ is the most frequent in the German language, as in English). [It is thought that such a machine was ordered from Dollis Hill, the Post office Research Laboratory, but it took so long to build that it was never commissioned. However, a more refined version of the ‘Rack’ was used successfully in the last year of the war, though it counted the appearance of common four letter words to increase the likelihood of finding the correct position. But Hut 8, the Naval Enigma team, did make much use for the same purpose of punched card equipment, run by the ‘Hollerith’ team, to count the occurrences of the very common word ‘eins’].

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