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Seventy Years Ago This Month at Bletchley Park November 1941Will the Defence of Moscow Hold? On 15th November the final German onslaught on Moscow begins. Though the Germans grind forward, in particular to the North and Northwest of the capital, a combination of the appalling weather and the ferocious defence slows them and finally the advance begins to peter out. Bletchley Park reads Enigma messages complaining that no German fighter aircraft had been seen in the air for two weeks. Stalin insists on holding the traditional Lenin-day parade, with the Russian reinforcements newly arrived from the East marching through Red Square and straight on through the city to join the fighting on the Western outskirts. The spearheads of the German advance come within a few miles of the capital and a few soldiers can see the spires of the Kremlin gleaming in the distance. But they are exhausted and the Germans casualties, for them, have been unprecedented with 85,000 killed on the Moscow front in this final assault. Elsewhere the Russians hold out and even throw the enemy back in the South, recapturing Rostov-on-Don on 26th November, the German’s first major reverse on the Eastern front. In besieged Leningrad people are dying in large numbers from the cold, hunger and the bombardment, but on 22nd November the ice road across the frozen waters of Lake Ladoga begins to operate and a thin lifeline is opened. Hitler worries that time is running out; his troops are not equipped for this winter fighting. However, the German Chief-of-Staff, Gen Halder, remains confident that the Russians are as exhausted as his German troops are; he writes in his diary on the 18th November “the enemy has nothing left in his rear”. The world holds its breath as it waits for the fall of Moscow and the collapse of Russia. Even the indomitable Churchill in his messages to Roosevelt admits he is planning for the worst. The Pacific Scene. A large carrier fleet has sailed from Japan, assembled in their Kurile Islands, and now on 26th November sets sail for some unknown destination, keeping radio silence. The British Empire in the Far East is on invasion alert, all too aware from decrypts of another Japanese force observed to be moving towards our Malay Peninsular. The Desert War. As a result of BP breaking Dolphin, the North Atlantic convoys are being successfully routed round the U-boat packs, so the convoy losses in the Atlantic have fallen dramatically and the number of U-boats sunk has increased. In the Mediterranean, the German and Italian shipping losses and the supply situation to North Africa have become unacceptable. So on 22nd November all U-boats in the North Atlantic are ordered to concentrate in the Gibraltar area and the Mediterranean, with another group forming in Norwegian waters to intercept the supply line to Murmansk. 20 U-boats pass through the Straits of Gibraltar into the Mediterranean in the next few weeks. One lucky side-effect of this change of policy is that it disguises from the German naval authorities that the fall in Allied shipping losses is due to the breaking by BP of the German main Home Waters Enigma key. The successes of the British air and naval attacks on the supply convoys in the Mediterranean are also due to code-breaking, in particular of the Italian navy C38m and of the Light Blue and Red Luftwaffe cyphers. But here it is much easier to disguise this by the use of very visible air reconnaissance, and the Germans are convinced that much of the information comes from our spies in the Italian harbours. At long last on 18th November General Auchinleck is ready to start his attack, Crusader. On the eve of the offensive the Enigma breaks reveal important information about Rommel’s re-dispositions and the strength of his armour. The British, or at least the Intelligence Officers at BP, are well aware that Rommel is expecting the offensive. Unfortunately by now the Africa Corps supply position has somewhat improved, due to the use of the route from the Balkans to Benghazi rather than from Italy to Tripoli that is very exposed to attack from Malta. But due to the work of BP, the British authorities in Cairo are receiving a continuous account of the enemy’s shipping arrivals and his losses en route to the African ports. They also have excellent information on the plans and state of the Luftwaffe in the Mediterranean, which helps greatly in the establishment of air superiority. The Desert Armies Y service has now broken the Africa Corps medium-grade field cypher and other army tactical codes, so that it is at last becoming possible to identify German units and formations. During the battle on the 28th November the capture of the key sheet for the month enables BP to complete its reading of Chaffinch, the German armies Enigma key for communications back to supply bases and which carries the daily appreciations to their HQ in Rome and Berlin, such as the German tank availability. And this capture also enabled Hut 6 to read one week of Phoenix, the Africa Corps operational communications Enigma key. These Enigma sources provided valuable information about the German order of battle and the location of most of Rommel’s units. But during Crusader Rommel also is very well informed about the activities and immediate plans of the British Desert Eighth Army because his Y service is reading the War Office high grade hand cypher, and continued to do so until January 1942. Rommel’s “Y” service is highly efficient and is greatly valued by him and the Africa Corps. The British are very careless in their use of vulnerable tactical codes and poor wireless procedures, General Freyberg sometimes horrifying his signals staff. And unfortunately the accurate tank returns now available to the British do not, in themselves, show the hard truth that our tanks are hopelessly inadequate, especially in their vulnerability to anti-tank gunfire, compared with the German armoured fighting vehicles. On at least three occasions before the launch of Crusader, Churchill had directed that General Auchinleck should be shown decrypts revealing the build-up of Rommel’s anti-tank strength. (In June 1942 a diplomatic decrypt from BP was to show Hitler describing the British tanks as “tin”. Regrettably this British weakness in tanks persisted throughout the war). And as the quite improper letter from the “wicked uncles” in BP to Churchill had described, only part of the intercepted traffic of the German North African cyphers could be read by BP, simply because they lacked enough teleprinter girls (called the teleprincess at BP) to handle the encyphered traffic that was involved in sending the intercepts from the Mediterranean to BP, and the decrypted information securely back again to the desert. Never-the-less the sheer amount of decrypted Intelligence information is at last enabling the British field Intelligence officers to make some forecasts about their enemy’s detailed intentions during Crusader. The battle does not go well for the British, but we keep on fighting to relieve Tobruk. The Breaking of the Abwehr Enigma. Since the spring of 1940 BP had been reading some of the hand-cypher traffic of the Abwehr, the German military secret intelligence service. Oliver Strachey carried out the work and his section has been named ISOS, Intelligence Services Oliver Strachey (though more usually known as his “Illicit Services” at BP). When the Italians gave up using their naval Enigma in early 1941, replacing it with the Hagelin C38m, Dilly Knox and his girls in the Cottage had started in the summer of 1941 to concentrate on the top Abwehr cypher, which used an unusual form of Enigma. Dilly specialised in Enigma machines that had no steckers, that is no plug-boards, as he had first broken an Enigma machine in 1937 that had no stecker, used by the Italians. The Italian naval machine was similar to this, though the feat of breaking the messages it carried was remarkable as the Italians rarely sent more than a few messages a day. Dilly used “rods” for this purpose, a technique he had developed which was unsuitable for the normal Enigma military machine unless the stecker board plugging was known. It was recognised that the Abwehr Enigma G had no stecker board, and Dilly and his girls soon worked out that it employed three code-wheels placed in the machine in different orders as instructed in the key sheet of the day, and effectively a fourth wheel as the reflector rotated, all four having different wiring from the standard five or eight wheels used by the German Services. The other distinguishing feature of this machine was that each wheel had several turn-over positions (11, 15, and 17 on the three wheels), providing a much longer cycle before repeating than the one-turnover per wheel found on all the military machines then in service. This was conceivably because the Abwehr machines often were needed to encypher long reports, compared with the normal Enigma message of, say, 250 letters. Dilly coins the names crab and lobster for simultaneous turnovers of the wheels, which are used in finding the key.
Remarkably soon, on 28th October Dilly was writing to the Director, Alastair Denniston, telling him that he had made great headway with the solution; he expected the recovery of the keys to be laborious and so asked for the return of his staff who had been seconded to help out in Hut 8 during the period when they were striving to break Dolphin, the German Home Waters Enigma key which was now coming out every day. David Rees and then Keith Batey come on secondment from Hut 6 in November, and Peter Twinn comes back from Hut 8 to take over the team early in 1942. But Dilly attributes their success in reading the first message on 8th December 1941 to his girls; in particular to Mavis Lever (who before long married Keith Batey) and Margaret Rock who carry out much of the hard work, finally unravelling the details of the machine and developing ways of regularly breaking the messages. The Abwehr Enigma was thereafter broken most days until a new machine was finally introduced late in 1944. The team expanded into Hut 16 and grew to be 100 strong. They attacked four Abwehr networks operating between groups of their outstations and their headquarters, each using a separate key. They employed four specially made “9 chain” bombes, of a type called Funf (a name that will be immediately familiar those who listened to Tommy Handley) that first came into service in November 1942. In total they made over 140,000 Abwehr Enigma decrypts. These were sent to M.I.6 where they proved to be particularly valuable in uncovering German spies and revealing how the Germans were falling for our double-cross misinformation campaigns, in particular at the time of the Normandy landings in June 1944. Dilly had warned the Director when he wrote on 28th October 1941 that he would be away for a few weeks, but sad to say, he was never able to return to BP as he was dying of stomach cancer. He carried on working, Margaret and Mavis liaising with him at his home, but he was to die on 27th February 1943. Before then Dilly had the pleasure of learning that his team, now under Peter Twinn to whom he had taught the arcane arts of his trade early in 1939, would continue to be called ISK, Intelligence Services Knox – a suitable tribute to a great cryptographer. The BP Management Crisis. On the 18th November General Ismay reported to Churchill that he had been “in touch with the Ministry of Labour and with the Department of the Admiralty which deals with Wrens, and gave instructions that the BP staff requirements should be given extreme priority”. This was a direct result of the “Turing Letter” sent by the four “wicked uncles” who were the senior staff in Huts 6 & 8 dealing with the decryption of Enigma. Quite improperly, they had sent the letter directly to Churchill on 21st October 1941. The three cases of staff shortages that they raised with the Prime Minister all directly impinged on their work on Enigma, but the new staff would not have come directly under their control. Inevitably the management structure at BP was very convoluted. The cryptographers were reliant on the work of some quite separate teams, sometimes in the Services like the bombe-girls who reported to the Superintendent of Wrens, First Officer Canale, to an Air-Force Sergeant E. Jones (who rose to be a Squadron-Leader) for matters related to the bombes, and to Harry Fletcher for liaison with Hut 6. The priorities for use of the bombes were sorted out in an informal manner between the heads of the two huts, two of the “wicked uncles”, Gordon Welchman in Hut 6 and Alan Turing in Hut 8; but in practice it seems that this was done by the other two, Stuart Milner-Barry in Hut 6 and Hugh Alexander in Hut 8 who were great friends, both being champion chess-players. (By this time Hugh was actually de-facto head of Hut 8, as Alan was not interested in administration). The Hollerith Hut was led by the formidable Freddie Freeborn, who formally reported, like Huts 6 & 8, to the Deputy Director, Commander Edward Travis. But to complicate matters the Hollerith team worked not just for the Enigma cryptographers but for any part of BP who needed punched-card equipment from time to time – such as the Dilly Knox team in the Cottage who were breaking the Abwehr Enigma; the C38m team in Naval Section who needed their help once a month; or the various teams working on tactical codes. It is said that the code-breakers tacitly left Freeborn to deal with the difficult issue of priorities for the use of his equipment. The picture becomes even more complicated when one remembers that the output from the Hut 6 cryptographers was going to a team of Intelligence Officers in Hut 3 many of whom were in the Services but were not formally part of the BP appropriate Service Sections under Josh Cooper for the Air Force and Colonel (later Brigadier) John Tiltman for the Army. At least the Hut 8 output was all going to the Naval Section in Hut 4 under Nobby Clarke, but in practice to Frank Birch as head of the Naval German Sub-section. No wonder the overloaded Director, Alastair Denniston, found it difficult to control this involved structure, and the same problems were mirrored in Whitehall where he reported to the Head of the SIS in the F.O. and to the Y Board, when the real “customers”, for all but the diplomatic output of BP, were in the Service Ministries. The Bletchley Park Trust welcomes the preparation of these notes, but the authors are responsible for the statements and the views expressed. |
