Seventy Years Ago This Month at Bletchley Park

October 1941

The Struggle for Moscow. The eyes of the world are now focused on Moscow. The expected final German assault begins on 2nd October in ideal weather and in an overwhelming force of  two Panzer Groups, containing 14 of her 21 armoured divisions, backed by three armies, some one and a half million men, with assured air superiority for by then only some 5% of the original Russian air force in Europe still survives.  To mount the assault Hitler has weakened, but not halted the attack on Leningrad. But the advance in the south continues with the fall of Odessa on the 16th and of Kharkov on the 24th.  At first General Guderian on the southern flank of the advance on Moscow, some 200 miles away, makes rapid progress, taking Vyazma on the 13th, encircling some 600,000 Russians.  His army reached Tula the next day, but had to by-pass the town due to the strong defence. They have now reached Borodino, the historic battlefield of 1812, 70 miles from the outskirts of Moscow.  If this rate of advance continues they will have reached Moscow by their target date of 7th November.  Panic breaks out in Moscow on 16th October as the government and party officials are seen leaving the city. But on the 19th Stalin declares a state of siege and announces that he will stay, stabilizing the situation in the city. General Zhukov has been summoned from Leningrad to take over the defence, and soon has the population marshalled, with a quarter of a million civilians throwing up three defensive lines round the city.  By the 19th snow has fallen in many parts of Russia, and the Germans are now facing appalling weather, with their tanks and trucks bogged down in a morass of mud.  They learn the hard way that there are a few weeks in Russia in autumn when road conditions become impassable, before the heavy frost hardens the roads. To their horror they discover that the much wider tracks of the Russian tanks enable them to move in these atrocious conditions far better than the German tanks can. The advance falters in the face of the weather and the numerous Russian counter-attacks; General Guderian fails to take Tula. By 30th October the advance has ground to a temporary halt, though soon the hardening frost and fresh supplies will enable them to move forward again.  Meanwhile on the 26th a Japanese carrier fleet has sailed for some unknown destination, unremarked by a distracted world.

Russian Sources of Intelligence.  Though the start of the offensive towards Moscow took the local Russian commanders by surprise, it was no surprise in Moscow.  It is probable that their “Red Orchestra” spy ring gave them ample warning, and it is certain that Britain was sending them copious information at this time.  The British were obtaining their information from Kestrel, the German army-air co-operation key in Russia as well as the old standby, the Luftwaffe Red Enigma key; from Rocket, the railways Enigma key; and above all from the Vulture key of the German armies in Russia. As early as 22nd September BP had predicted the resumed thrust on Moscow from the Kestrel decrypts which showed that most of General Kesselring’s Luftwaffe formations from the Northern front, together with Panzer divisions from both North and South were being transferred to the Central front armies facing Moscow.  Between 20th and 24th September a series of nine warnings had been sent from Whitehall to Moscow. (Churchill, perhaps with good reason, never entirely trusted “C”, Sir Stewart Menzies, to have sent material on to Moscow. He minuted him on 2nd October: “Are you warning the Russians of the developing concentration on the central front?  Show me the last five messages you have sent out on the subject”). Once the offensive began there was a big increase in the number of Vulture messages deciphered by BP.  The Enigma decrypts ensured that Whitehall, and so Moscow, was fully and promptly informed of the scale & fortunes of the offensive.  But perhaps the most valuable information of all came from Richard Sorge, their remarkable spy in Tokyo. He was a German journalist who edited the daily newsletter in the German Embassy in Tokyo. In his last great service to Russia before he was arrested on 18th October, he informed his masters in Moscow that the Japanese planned to attack south into the Pacific against the Americans, not against the Soviet Far East at least until the spring of 1942 at the earliest.  This was confirmed by signals intercepts, so Stalin believed it and began transferring his armies in the East to the defence of Moscow. (The confirmation probably came from the UK from the reading of Japanese diplomatic traffic from Tokyo to Berlin using the “Purple” machine given to BP by the Americans who had broken into it in the autumn of 1940).  The first of the Russian troops arrived from the Far East at Borodino in mid-October just in time to try to halt the German advance.
 
British Intelligence in the Mediterranean Theatre.  There is an uneasy peace in the desert as General Auchinleck prepares for his Crusader offensive, which will be finally launched on 18th November.  Churchill fumes at the delay, for he knows from the decrypts that the Africa Corps is desperately short of supplies, but that Rommel’s situation will improve as the Russian front goes quiet, releasing reinforcements for the Mediterranean.  The British obtain much of their Intelligence information from the Enigma decrypts.  As well as the Luftwaffe Red they are reading the Luftwaffe Light Blue operational key for Africa and Mustard, a key used by the Luftwaffe Y service, which is valuable for warning our own forces about their poor security. In September BP had first started to read the Africa Corps Chaffinch II key used for communication with their higher authorities in Rome and Berlin.  BP reads it regularly until the 19th October, but only with considerable effort and often a week or more late. Never the less it proved invaluable for providing German order of battle information for the forthcoming offensive, and it established certain important German re-dispositions on the eve of the British offensive. (In due course BP came to recognise that each evening Rommel’s HQ would send a situation report to Rome prepared by his Chief Operations Officer; these were invaluable as summaries of the situation as seen by Rommel’s HQ, but also proved to be valuable to Hut 6 for apparently the words “An Ida Bison”, that is “Chief Operations Officer”, invariably appeared somewhere in the text, providing an excellent crib).   For the first time, the Allied estimates of the Axis strength in the desert in tanks and aircraft were remarkably accurate; for example Military Intelligence estimated before the battle that Rommel could deploy 385 serviceable tanks when the actual number proved to be 390. The steady build-up of detailed information on the enemy forces carried out by Hut 3 and the Military section at BP was at last paying dividends. And at last some information on the Africa Corps’ strategic plans was becoming available, thanks largely to Chaffinch.

However, it was in the unglamorous but vital field of supplies to North Africa that the work of BP was making the most dramatic contribution at this time. The decrypts revealed that Rommel’s supply position was becoming increasingly precarious, both because of the effectiveness of the Allied attacks on his supply shipping, and because the Russian campaign was taking priority for supplies.  Because the Luftwaffe provided air cover for convoys, the Luftwaffe keys were the source of much information on them, but the most valuable source was the Hagelin C-38m, used by the Italian navy and first broken by BP in June 1941.  At the beginning of each month Hut 8 would break the new settings for the month, which at first took several days but became faster each month. (By October it was taking three days or less). The Italian section of Hut 4 under Prof E.R.Vincent did the rest of the work, his girls inevitably, if grossly unfairly, becoming known as the “Hags”.  These decrypts not only gave warning of the shipping movements, but also frequently told what was being carried in each ship.  The RAF operating from N. Africa and Malta could then send out reconnaissance aircraft to be seen, and so provide an explanation for the good Intelligence. Only then could the RAF and the Navy set about attacking the convoys, concentrating on the most valuable cargos.  On 21st October 1941 some surface ships, Force K, are re-established at Malta. “Its exploits …were to be an outstandingly successful exercise in the operational use of intelligence” concludes the Official Historian.  As well as the direct attacks on the convoys, the bombing and mining of the ports used by the Africa Corps often followed from decrypt information about the imminent arrival of important supplies.  (The RAF successfully attacked a ship in Benghazi before it could be unloaded, containing the entire stock of a particular type of bomb).  By now the monthly Axis tonnage sunk is twice what it had been before the C-38m was broken.  The decrypts showed that Rommel was short of water, food, and fuel as well as of ammunition. It is now known that he was forced to postpone an attack on Tobruk from September until late November – by which time Auchinleck had at last launched his offensive.  Churchill made much use of these decrypts in trying, unsuccessfully, to persuade the C-in-C to bring forward his offensive.

BP Codebreakers write directly to Churchill.  On the 21st October Stuart Milner-Barry delivers a letter in person from four of the BP senior cryptographers to No.10 Downing Street.  Eventually he is let in to see Churchill’s PPS, Brigadier Harvie-Walker. At first Harvie-Walker is very suspicious of this strange individual who has forgotten to bring any official identification but refuses to give any details of the contents of the letter beyond stating that it concerns a matter of great national importance which he could not discuss with anyone who is not authorised to know.  Finally when Stuart explains that he had met Churchill during his visit to Bletchley Park on 6th September, Harvie-Williams is persuaded to agree to place the letter before the Prime Minister.  Alan Turing, Gordon Welchman, Hugh Alexander and Stuart Milner-Barry, the four senior cryptographers concerned with the breaking of Enigma, who became known as the ‘Wicked Uncles’ by the junior staff apparently, signed the letter in that order. Alan Turing is the titular head of Hut 8, the naval Enigma cryptography hut, the man primarily responsible for the concept and building of the bombe, the machine that is enabling BP to perform “the impossible” by breaking Enigma keys, and by now “the Prof” is considered the chief scientist and leading mathematical brain of BP who contributed ideas to many aspects of the work. Hugh had started in Hut 6 but has now been moved to Hut 8 where he acts as the de-facto head because Alan Turing is not good at the managerial and administrative side of the work. Gordon Welchman is the head of Hut 6, the Enigma cryptography hut, and had been the person who had the vision that led to the setting up of these huts and the formation of what was essentially a production line for making Enigma decrypts. Stuart Milner-Barry is his deputy and primarily responsible for the vital “cribs” side of the Hut 6 work; in 1943 he was to take over responsibility for Hut 6 when Gordon became Assistant Director responsible for the mechanisation work of BP. All four had been at Cambridge, Stuart as a classicist, and the other three as mathematicians. Alan was aged 29 and the others up to 6 years older.  They knew each other well, Gordon and Stuart having been undergraduates at Trinity College together. Alan and Hugh were from Kings College though Hugh had gone down in 1931, the year Alan came up. Hugh and Stuart were playing chess for Britain in Argentina when the war broke out and they now reside together in the “Shoulder of Mutton” Inn in Old Bletchley. When war broke out Gordon had been a lecturer in mathematics at Sidney Sussex, and Alan a research fellow at Kings.  Stuart had been a stockbroker and the chess correspondent of The Times; after the war he had a distinguished career as a civil servant.  Hugh Alexander had been a schoolmaster and then Director of Research at the John Lewis Partnership.  After the war Alan Turing went to the National Physical Laboratory to lead the national drive to build a computer, ACE, but he transferred to Manchester to work on the Mark 1 because the work on ACE went so slowly. Gordon took Hugh’s place at the John Lewis Partnership, before moving to MIT, teaching the first course on computers there.  Hugh Alexander went to Cheltenham with the successor organisation to GC&CS, called GCHQ.

The letter is often called “The Alan Turing letter” but it seems more likely that Gordon Welchman drafted it, though Alan would certainly have taken the view that the highly irregular approach to the Prime Minister was the natural way to proceed.  They first remind the Prime Minister that he met them when “you paid us the honour of a visit” to Bletchley Park, which had taken place on 6th September 1941. (In fact the first two or three of the signatories had probably met him in July when they were summoned to the Foreign Office to each receive a cheque for £200 as a reward for their exceptional services).  They then write that “thanks largely due to the energy and foresight of Commander Travis we have been well supplied with the ‘bombes’ for the breaking of the German Enigma codes”. No doubt this is intended to avoid appearing to criticise him, and indeed they end the letter by explicitly stating that he “has all along done his utmost to help us in every possible way”. But it reads strangely in view of the dreadfully slow progress in building up the number of bombes, though at the time when they were writing the number available is increasing rapidly and was to reach 16 by the end of the year. The essence of their letter is to plead for more staff for the two Huts 6 & 8, for the Hollerith punched card section in Hut 7, and for more WRNS who had been promised in July to take over the testing of what they call “the stories produced by the bombes” but who had still not appeared.  The very next day, 22nd October, Churchill minutes his Chief of Staff, General Hastings Ismay under an “ACTION THIS DAY” sticker: “Make sure they have all they want on extreme priority and report to me that this has been done”.  As a result of this the BP staff requirements were thereafter given extreme priority. 

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