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Seventy Years Ago This Month at Bletchley Park
August 1941Hitler’s Fatal Mistake? Almost unnoticed by the depressed British public several events in August 1941 provide the first signs that the tide may be turning. Hitler orders a halt to the offensive towards Moscow, in order to reinforce the drive to the important oil-fields in the South. Despite the continuation of the German advances in the North to cut off Leningrad and in the South into the Crimea, the decision to delay the advance on Moscow was seen in due course as leading to the failure to take Moscow in 1941. In the Atlantic the Allied shipping losses fall dramatically, due primarily to the mastery by BP of the cypher used by the German submarines enabling the Admiralty to route the convoys round the wolf-packs. The first of the North Cape convoys carrying desperately–needed supplies to Russia arrives safely in Murmansk. Across the Atlantic Churchill confers with Roosevelt. The Atlantic Charter that emerges may be little more than rhetoric, but this first building of the friendships between the leaders and their staffs that are initiated on board the ships off the coast of Newfoundland is to bear fruit in joint endeavours which became fully operational once the USA entered the war with the Japanese assault on Pearl Harbour four months later. That much heralded yet surprise event can now be seen to have been an almost inevitable consequence of the US/UK decision to impose an embargo on supplies of oil to the proud Japanese. Doubts Multiply in the German General Staff in Russia. The German assault in Russia had now taken longer than any previous German offensive of the war, and despite their continuing sweeping gains, there is mounting evidence that all is not going well for the Germans. Their armoured formations are suffering as much from unservicability in the Russian conditions as from the many counterattacks by the Russian army and their numerous partisan groups. The major Russian counterattack in the vicinity of Yelnya rages for much of the month. For almost the first time the German army encounters enemy tanks used sensibly in ambush tactics, not headstrong frontal assaults, and finds that the few Russian T34 and KV1 are superior in reliability, fire-power and frontal armour to the German current models; despite the Russian poor tank communications, the Russians are gradually learning to handle the Panzer attacks. Germany had invaded Russia with over 5,000 tanks but lost 2,700 in Russia in 1941 and only produced some 1500 replacements during that year. They suffered a steady decline in vehicle strength as the summer dust wore out the engines, even before the autumn mud took its toll of the running gear. The Russian tanks were simpler and more rugged in design, with broader tracks that could withstand the Russian conditions better. Hitler’s decision to halt the thrust on Moscow, to reinforce the attack towards the industrial belt of the Donetz basin and the oil fields of the Caucasus, brings immediate rewards as the campaign in the South goes well. In the North the Germans have now almost cut off Leningrad, though the Finnish forces resist German pressure to advance further once they have reached their pre-1939 frontier. But the German High Command is very split on whether it is wise to delay the assault on Moscow, with the first murmurings of dissent over Hitler’s leadership amongst his generals. For until Moscow falls Russia seems unlikely to sue for peace, and can this now be achieved before the snows come? Churchill sends a steady stream of letters to Stalin, informing him of the steps the UK is taking to help the Russians. Most of these go unacknowledged, but in his very first reply on 18th July Stalin requests that the UK should create a new front in Northern France, or in Norway where Russian would co-operate. Churchill comments in his history of the war “This theme was to recur throughout our subsequent relations with monotonous disregard for physical facts. … The Soviet Government had the impression that they were conferring a great favour on us by fighting in their own country for their own lives. The more they fought the heavier our debt became. This was not a balanced view”. To try to divert some of the Luftwaffe back to Western Europe, the RAF begins fighter sweeps across Northern France on 7th August. On 15th August the reduced local Luftwaffe strength encourages Bomber Command to try a daylight raid on a power station near Cologne, but suffers considerable losses. Churchill agrees to despatch 200 much needed Tomahawk fighter aircraft to Russia, and large quantities of rubber, tin, wool, lead, etc: “We endured the unpleasant process of exposing our own vital security and projects to failure for the sake of our new ally – surly, snarly, grasping, and so lately indifferent to our survival…Our Service Departments felt it was like flaying off pieces of their skin”. On 21st August the first British Arctic convoy leaves Icelandic waters for Russia, reaching Archangel at the end of the month intact. Britain continues to get much of its information on the Russian front from the reading at BP of the German army Enigma key, Vulture. They had broken an army ground-air Enigma key, Kestrel, in July and then broke three further versions (Kestrel I, II, III) during August. Churchill denounces atrocities in Russia. On 24th August in an emotional broadcast Churchill denounces the German atrocities behind the lines in Russia: “We are in the presence of a crime without a name…Since the Mongol invasions of Europe there has never been methodical, merciless butchery on such a scale”. It was, perhaps, the only occasion when Churchill endangered the BP secret by making public use of information that had come from decryption of signals. BP was horrified but perhaps Churchill felt there were other feasible sources for the information reaching him. Though there is no direct evidence of cause and effect, three weeks later on 13th September BP did decrypt an order to the German Police leaders in Russia warning them of the danger of decypherment of their signals and ordering them to make use of couriers when sending figures of executions. German Police cyphers changed later that month, replacing double transposition with double Playfair, (a name deriving from that of the British Admiral of the 19th Century who invented the method). However this proved not to be the disaster that it might have been for BP as the Military Section under Colonel John Tiltman promptly uncovered how these new hand-cyphers operated and continued to break them most days. Liaison with the USA. Churchill sails in the British battleship, Prince of Wales, to meet President Roosevelt in the cruiser Augusta, off the coast of Newfoundland on 9th August. (On the journey he read the novel “Captain Hornblower R.N.”, and sent a message to Cairo “I find Hornblower admirable”. This caused some perturbation in the Middle East HQ where it was imagined that “Hornblower” was a code-word for an operation about which they were uninformed!). Of course the USA is still a neutral country, but Roosevelt is now taking remarkable steps to aid the British and their new allies, the Russians, - safe in the knowledge derived from decrypt information passed on by the British that the German policy is to avoid upsetting the USA. Perhaps the main value of the conference was that it enabled the leaders and their staffs to get to know their opposite numbers and to start on the programme of joint planning that was to be such a feature of the conduct of the war after the US entry following Pearl Harbour. One outcome of the discussions was that the USA took over responsibility for security of shipping in the America-Iceland stretch of the Atlantic thus relieving the British navy. The Director of BP, Cmdr Alastair Denniston, flew into Washington on 10th August, at the time of the meeting off Newfoundland, aboard an airplane of the US Army Air Corps. Denniston had been sent to meet the leading US cryptographers to attempt to smooth out the frictions that had arisen between the two sides since the visit to BP of four US cryptographers in January 1941. The US visitors had delivered a “Purple” machine to BP, which enabled them to break the Japanese diplomatic cypher. Some of the US cryptographers considered that the UK had not reciprocated, even though BP had sent detailed documents about Enigma and its code-breaking methods. (These probably included parts of Alan Turing’s “Prof’s Book” and the Americans had good reason for complaint if the problem was that they did not find this manual entirely easy reading). One of the areas of conflict was the US request for a bombe. Even the fact that the written request named the bombe horrified the security conscious staff at BP. Denniston had planned to explain to the Americans that BP had only got 6 precious bombes, but “C”, his boss Sir Stewart Menzies, vetoed this because it might provide the US with an excuse to argue that they should manufacture the machines in the USA. It would appear that the British attitude to cooperation was an uneasy mixture of the desire to have the US experts help, but fear of loss of control of the operation. They were very conscious of what they considered, sometimes with good reason, the poor security consciousness of the US. However, Alastair Denniston was able to make friends amongst the US army cryptographers, in particular with William Friedman, the veteran cryptographer and head of the Army team in the Munitions Building. One of Friedman’s assistants, Frank Rowlett who had played a major part in breaking Purple, has recorded how much they admired Denniston, both as a person and as an outstanding cryptologist – which was praise from Caesar indeed! In this visit Denniston undoubtedly helped to establish the basis for future close relations with the US Army cryptographers. But Denniston does not seem to have got on so well with the US navy team in Arlington Hall, where Mrs Agnes Driscoll, a veteran cryptographer, claimed she had a method for breaking Enigma; Denniston failed to convince her it would not work. The Punched Card Installation at BP. Some punched card equipment had been used by GC&CS at BTM Co (at that time jointly owned by Hollerith and IBM) for cryptographic purposes in pre-war days. An initial installation had been set up just outside the wire at BP in April 1940 using staff from BTM. By mid-1941 the scale of the effort in Hut 7 at BP using “Hollerith” equipment under the firm leadership of F.V. (Freddie) Freeborn, deputy Ronald Whelan, had much increased but was still on a much smaller scale than that used by the Americans. There were probably about 45 pieces of equipment at this time, manned by a staff of over 50. One of the most important pieces of equipment was the IBM 405 alphabetic Tabulator, of which a large number were directly shipped to BP from the US. (When the large crates were opened gifts of much welcomed food supplies were generally found). In November 1942 they moved into the purpose built Block C, and by mid-1943 were using some 145 pieces of equipment with a staff of about 140. An out-station was built-up in The Lodge at near-by Drayton-Parslow for the creation of cryptographic material for the Code & Cypher Compilation Unit at Oxford that came under BP, such as one-time pads and TypeX settings, using staff housed in a hostel in the grounds along with an operator training school. By the end of the war the Hollerith team consisted of over 500 people, of whom many were Wrens, consuming 2 million punched cards per week. The installation is used for jobs from most sections of BP, but probably primarily for the support of the hand-cypher teams. The top-priority tasks every day are for Hut 8, first to locate repeats occurring between naval Enigma messages for “Banburismus”, a procedure designed to reduce the possible wheel orders to save bombe time; and then, once the wheel order and stecker settings for the day have been found, using the “Eins” catalogue to recover the individual message indicator setting. There are special routines to help with Playfair decryption, and monthly there is a large priority job to run the Hagelin catalogue for the Italian navy C38m settings. German Naval Enigma Broken. For every day of August 1941 Hut 8 breaks the Enigma settings for the German main naval key, called Dolphin by BP, and with a delay acceptable for operational purposes. Because at this time the German navy only change the wheel order settings every other day, and now that one of the six bombes at BP can be dedicated full-time to Hut 8 work, during August settings are recovered within 72 hours for the first day and with well under 24 hours more work for the second day of the pair. During July key sheets captured from the trawlers and the U-110 had eased the work. But as Alan Turing had predicted, once they had reconstructed the bigram tables used for the encryption of the indicator settings, which had changed on 15th June, their cribs now prove good enough to be able to find the settings cryptographically. It has been galling for them to struggle without much success over the months while their colleagues in Hut 6 are breaking the Luftwaffe keys daily with seeming ease. But the German navy is far more security conscious than the other Services. As well as using tables to disguise the indicator settings, which means that Hut 8 has to solve each individual message setting until they have reconstructed the tables, the German navy employs a choice from 8 code-wheels to fill the three positions in the machine, when the other Services use a choice from only 5; that means that it would take on average almost six times as much bombe time to find the settings, up to 80 hours unless Banburismus can be used. Hut 8 knows from a June decrypt that the Germans plan to introduce some change in the Enigma machines on the U-boats, but for the moment they can delight the Admiralty by providing a steady stream of valuable information, particularly about the positions and movements of the submarines. This great achievement went on almost every day for the next six months. Meanwhile on 30th August in Germany, an army cypher clerk makes a mistake in sending a four thousand-character message on a new teleprinter cypher machine, Lorenz SZ42, which will lead to BP reading the very top German messages. The Bletchley Park Trust welcomes the preparation of these notes, but the authors are responsible for the statements and the views expressed. |
