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Seventy Years Ago This Month at Bletchley Park February 1941Short-Lived Victory in the Western Desert.On 7th February the jaws of General Wavell’s pincer-movement close on the Italians at Beda Fomm in the Western Desert. Relying on decrypt information, General O’Connor has taken the daring but direct desert route to get between the Italians and their supplies, and the Australians coming along the coastal road force them into the arms of the British 7th Armoured Division. In the short campaign the Italians have lost 20,000 killed or wounded and 130,000 prisoners. But now an uneasy pause develops with the expected continuing British advance to Tripoli to throw the remaining Italians out of North Africa not materialising. For General Wavell, on direct instructions from Churchill and the Chiefs-of-Staff in London, has had to withdraw some of his best troops from the desert to meet the anticipated German invasion of Greece. General Rommel arrives in North Africa on the 12th February, and the first elements of the German Africa Corps are not far behind. But General Wavell is not unduly alarmed for, judging by British experience, it will take at least until the middle of April before they are ready for battle, will it not? Intelligence Information on the German Moves in the Balkans. For the first time after nearly 18 months of disastrous war, the British Intelligence services are able to anticipate the German strategic plans with some accuracy. From reading the Luftwaffe Red Enigma messages Britain is able to predict the forth-coming invasion of Greece, and even to name the date when the Germans plan to cross the frontier as 12th March. Churchill had been anticipating this move for some weeks and had persuaded the Defence Committee that the Germans would attack Greece on 20th January. He used the rather perverse argument that “Nothing would suit our interest better than that any German advance in the Balkans should be delayed till the spring. For this very reason one must apprehend that it will begin earlier”. However, our intelligence services are still convinced that Hitler intends to invade Britain in the approaching spring, when Hitler had long ago turned his attention to the East. It is perhaps as well that we had a Prime Minister who was often wiser than his advisors. (In defence of our intelligence staff, Hitler had ordered that the preparations for the invasion of Britain should be kept alive as a deception to draw attention away from his plans for the invasion of Russia). Then on 7th February 1941 BP breaks the new version of the German railways Enigma, known to Hut 8 and the Military Section at BP as the Rocket key, first used in the Balkans on 23rd January. Once the “Railways Research Service” had been brought in to elucidate the nature of the pro-forma material that emerged, a new, powerful, source of information on the German movements to the Balkans and the Eastern front becomes available. It is not the fault of BP and the Intelligence Services that, unknown to them, Hitler has now decided to postpone the date from 12th March until 1st April, though there is a lesson to be learnt from this change that will often be repeated: decrypt information may well be absolutely reliable at the time it is generated but the plans of the enemy, and especially the dates of operations, may change before they are executed. The German move into Greece is partly designed to help their beleaguered Italian ally, but also to secure the flank of the German armies that will become exposed from Greece when the planned assault on Russia is initiated. General Wavell protests most vigorously at having to withdraw some of his best forces to go to the help of the Greeks, just when he has the Italians on the run, believing that the Germans are bluffing over Greece to stall the British advance in Libya. In any case he feels an operation in Greece is most unwise. And history seems to prove that he was right, if only because the Germans failed to mount their invasion of Greece until 6th April. What might have been if only Wavell had been allowed to maintain his advance in Libya for just a few weeks more! Intelligence Information on the German Moves into North Africa. By February it is all too clear that the Luftwaffe has come to the aid of the Italians by moving into Sicily and now Libya. On 27th December 1940, on the basis of Luftwaffe Red key decrypts by BP, Air Intelligence warns that Luftwaffe attacks on the Mediterranean fleet are to be expected in the near future. Unfortunately, for some reason, this timely warning is not passed on by the Admiralty before the fleet is attacked with damage to the carrier HMS Illustrious on 10th January, and to the cruiser HMS Southampton which was sunk on the next day. From now-on the Luftwaffe decrypts by BP enable the Air Intelligence service to keep the Mediterranean commands informed of the scale and deployments of the Luftwaffe. (Unfortunately it took months before the equipment and staff would be deployed to enable the naval ships themselves to read the Luftwaffe tactical signals that would provide warning of imminent air attacks). Then on 9th February BP decodes a message instructing the Luftwaffe to escort convoys assembling in Naples to go to Tripoli. BP correctly deduces that these convoys are to carry units of the German army to Libya, but the Air Ministry and the Admiralty only accept this with great reluctance, as they wish to believe that these are ships going to evacuate the Italians from North Africa. General Rommel arrives in Libya on 12th February followed closely by the first units of his Africa Corps. On 22nd February their arrival is confirmed when a British recce patrol makes contact with a few German armoured cars. By a strange co-incidence Lieutenant Edgar Williams, the young officer who first spots that small German advance force at El Agheila, is to rise rapidly to become General Montgomery’s distinguished Chief Intelligence Officer, ending the war with the rank of Brigadier and a well-earned knighthood. Breaking of the Light Blue. In preparation for the arrival of Luftwaffe squadrons in North Africa the Germans introduced a new operational Enigma key for army-air force co-operation in that area at the end of January 1941. With the arrival of their aircraft the traffic mounts, and BP (Hut 6) breaks this key, which they call the Light Blue, on 28th February, reading it regularly within 24 hours every day until it was replaced on the first day of 1942 by other keys (which BP promptly broke). So now BP has broken seven different Enigma keys, and is obtaining Intelligence not just of strategic value from the Luftwaffe Red (and from Rocket, the Railways Enigma), but also information of immediate operational value to the Commanders in the field in the Western Desert from the Luftwaffe Light Blue – if only a way can be found to get round the delays involved in feeding the decrypt information generated by the Intelligence team in Hut 3 at BP to those in the field, who need it fast. For established protocol requires that Hut 3 pass their decrypt information from these Luftwaffe sources on to the Air Intelligence branch for evaluation, who may agree to pass it on to the appropriate Whitehall Army or Navy Intelligence branches in London before it can be transmitted by them to the field commanders. This is a bureaucratic challenge to which the traditionally procedure-bound British will have to rise in the hour of need of their desert army! The Meteorological Sub-section at BP and the Breaking of the German Naval Weather Code. At the opening of the war all the belligerent countries have started to code or encypher the messages that carry their raw metrological information and their service weather forecast broadcasts. BP has a team, working in Air Section, which attempts to read these cyphers for the information is of obvious operational value for weather forecasting. The problem is that, though the messages are usually relatively simple book-codes, using the International Meteorological Code format as a basis, there are large numbers of them, and the information has to be extracted with next to no delay if it is to be of any operational value. It absorbed an ever-increasing amount of effort at BP, the Meteorological Sub-section under Dr George. C. McVitie being housed (rather surprisingly) in Hut 8, though they moved to the new Hut 10 taken over by Air Section at about this time. McVitie was a mathematician (King’s College, London) and meteorologist on secondment from the Met Office, who has been described as “tall, thin, professorial, unkempt, with a fine head of hair and a high voice, always jolly, never upset, good to his subordinates, and with a mind that absorbed everything quickly”. His small, grossly overworked, team consists of some 10 staff at this time, mostly seconded from the Dunstable Meteorological Office. As well as German and Italian, they are tackling Russian, French, Spanish, Syrian, and wanted to take on meteorological signals of other neutral states in Europe and the Far East (Japan) if only they had the effort to spare, partly because of the cribs these would provide. On 8th February 1941 the team breaks the main German naval meteorological cypher, and thereafter breaks it regularly, though with gaps when the Germans change the codebooks. It was called Germet 3 at BP (but also was often referred to as “DAN”) and was used for messages from the various German Met. Stations to a centre at Norddeich in North Germany, where a powerful radio transmitter, call-sign DAN, sent out the collected weather reports in the same cypher. At BP it is recognised that the reading of this particular cypher might prove to be of exceptional value for the team in Hut 8, who are trying to break the German navy Enigma, once it is realised that parts of these meteorological messages have originated from U-boats in the Atlantic. These weather messages from the U-boats have first been encoded using a special “Weather Short-signal Code-book” and then have been re-encyphered in the submarines’ current Enigma key. If only BP had the short-signal codebook they could now recreate the encoded form of the weather messages from the U-boats as they had been before they were encrypted, so providing excellent cribs for this vital Home-waters Enigma key, called Dolphin in Hut 8. But could BP recreate or capture that codebook? It is the meteorologist Philip Archer from Hut 10 who acts as the liaison officer with the Hut 8 team, and so inevitably the use of these weather cribs becomes known at BP as “Archery”. US Visit: Purple Machine given to BP. In December 1940 the US and Britain had signed an agreement in Washington which covered the exchange of complete technical information about Japanese, German, and Italian codes and cyphers. As a result a party from the US arrives in the UK on the 8th February aboard the new British battleship HMS King George V. Cmdr Edward Travis, Deputy Director of BP, and Col John Tiltman, head of the Military Section of BP, meet them at the docks. They are driven to BP where they are received by the Director, Alastair Denniston, and the senior staff, and then on to the mansion at Shenley Park, near Bletchley, where they are to be entertained in some style during their five-week stay. As well as visiting many parts of BP, they are shown the Admiralty’s Operational Intelligence Centre where the U-boats are tracked, the Naval Y stations at Scarborough and Flowerdown and a radar station at Dover. The US party consists of two US army cryptographers, Capt. Abraham Sinkov & Lieut Leo Rosen, and two US naval officers, Lieuts. Robert Weeks & Prescott Currier. The leading US cryptographer, William Friedman, is unwell and so unable to come at this time. It was in November 1934 that Hugh Foss and Oliver Strachey of GC&CS had made the first break into the Japanese Type A diplomatic cypher machine and had built an “emulator” (the “J machine” made by the Metropolitan Police wireless staff at Denmark Hill) to assist with the decipherment of the signals. Captain John Tiltman had broken the signals of the Japanese military attaché in 1933, and new Japanese military cyphers in 1938 (while working at Bletchley Park during the temporary move of GC&CS there during the Munich crisis). But with the coming of the war, the effort at BP had to be largely diverted to the struggle to read German Enigma, and it was the US Army team in Washington, under the overall leadership of the great veteran cryptographer William Friedman, who made the first break into the new Japanese Type B diplomatic cypher machine, known to the US as Purple, on 27th September 1940. As soon as they had uncovered its architecture they commissioned a young electronics engineer, Leo Rosen, to construct a machine that would emulate its operation. This he had done in remarkably quick time, and he now brings one of these “Purple” machines, one of only three so far built, to present to BP. As so often seems to happen, the real experts have no difficulty in working well together in mutual respect, despite the sometimes-appalling lack of co-operation shown by their military and political bosses. The Bletchley Park Trust welcomes the preparation of these notes, but the authors are responsible for the statements and the views expressed. |
