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Seventy Years Ago This Month at Bletchley Park May 1941A Further Month of Very Mixed Fortunes. In the Western Desert Rommel has outdistanced his supply-lines so he has to pause to let his exhausted troops recover at the frontier to Egypt, as Enigma decrypts reveal on 6th May to the anxious British staff in Cairo and Whitehall. The ever-impatient Churchill goads General Wavell on to the offensive to throw the Africa Corps back from the frontier. On 15th May Wavell launches a premature attack and is forced to halt after a few days, but does recover the important Halfaya Pass. At the end of the month Rommel attacks again and retakes the Pass but is ordered not to go further. The expected airborne invasion of Crete commences on 20th May, but to the despair of those few who know that we have the complete plan-of-attack due to the work of BP, the Allies are unable to hold the island and after heavy fighting have to evacuate at the end of the month. At sea off Crete the naval losses due to air attack have been horrendous, and in the Atlantic the shipping loses are mounting as the U-boat attacks multiply. But with the capture of the weather ship München on 7th May and the U-110 on 9th May, the documents recovered take BP to the point of being able to read the all-important naval Enigma key, Dolphin. After a chase aided by the work of BP, the British finally sink the German battleship Bismarck on 27th May. This victory serves to lift the battered morale of the British public, who have suffered badly in the “Spring Blitz” with severe air raids on every night of the first ten days of the month. The ever improving countermeasures lead to 23 German aircraft being shot down on Humberside on 7th May, and the next day Derby escapes the treatment of Coventry with the help of “beam-bending”. Finally on 10th May London is subjected to one of its most severe raids, with the debating chamber of the House of Commons destroyed, many streets closed, and 1,436 civilians killed – more than in any other single raid on Britain. Londoners might have felt some comfort had they known that these raids are intended by Hitler to distract attention from his mounting build up in the East, and that the terrible raid on London marks the Luftwaffe bombers farewell gesture before they depart to prepare for the assault on Russia. If Stalin is fooled his actions do not show it, as the frantic Russian defensive measures along the frontier are accelerated, though he also does everything possible not to provoke Germany. The British public knows nothing about these developments, but their Government is well informed due to decrypts; unfortunately the German Government is also well informed, reading some of the messages from the British Embassy in Moscow to London, and so learns about these counter-preparations. Crete. Since the end of March Enigma decrypts have left no doubt that Germany is concentrating airborne forces in the Balkans, though where the target is to be is uncertain. Germany tries to plant the belief that the aim is to capture Malta, and makes air raids there to that end. On 6th May Enigma decrypts confirm that the real target is to be Crete with full details. General Student, in charge of the airborne troops of the German Fliegerkorps XI drew up the plans, and Hitler approved them after some hesitation on 21st April, for launch on the17th May. Churchill had been expecting this for some time, and had given orders for defences to be prepared there as long ago as November 1940, though unfortunately these had not been executed with much vigour. The excellent information is obtained because the German airborne troops are part of the Luftwaffe and so send their messages using Luftwaffe Enigma keys. At this time BP is reading two Luftwaffe keys but not any Army keys, though they are soon to do so. The link carrying decrypted Enigma messages from BP to Cairo was extended to Crete by 18th April. General Bernard Freyberg VC took command in Crete on 30th April, receiving material from BP but disguised as information obtained by a well-placed spy in Athens. Whether General Wavell, who went to see him in Crete on 30th April, told him the true origin of the stream of accurate information he was receiving will never be known. (It is known that, many months later in the Western Desert, Freyberg was to make a casual enquiry as to whether that excellent spy was still performing). For the first time but not unfortunately the last, the senior staff in BP, who know that Freyberg has been given the full details of the German plan of attack with daily updates on the Germans own reports on their progress, watch in disbelief as the battle develops and this huge advantage fails to avert yet another British defeat and evacuation. It is sometimes said that Freyberg failed to deploy his forces properly to meet the airborne threat because he was anxious to disguise that he had the enemy’s plans from Enigma decrypts. But those plans were so much in accord with what the British planners had predicted anyway, that this does not seem to have been a significant factor. It is also said that Freyberg misread one of the crucial Enigma messages, and focused on opposing the secondary sea-borne landing rather than the primary air-assault. It was recognised in good time in London that this seemed to have happened from his planning, but apparently the warnings from the Prime Minister were ignored. “In no operation did I take more personal pains to study and weigh the evidence or to make sure that the magnitude of the impending assault was impressed on the C-in-C and imparted to the General on the actual scene” Churchill wrote after the event. The staff officer flown out to Crete to brief Freyberg on the accumulated Intelligence subsequently ruefully put the famously brave Freyberg in the “Bear with Little Brain” category. On 15th May the Germans postpone the assault until 20th May, but Freyberg learns this from BP within 24 hours. On the morning of 20th Colonel Monty Woodhouse was having breakfast with General Freyberg when “I looked up and saw the blue sky full of German aircraft…The General continued quietly eating his breakfast. What should I do? It seemed impolite, not to say insubordinate, to interrupt. Finally I plucked up the courage to speak to him, Freyberg raised his head, grunted, and then looked at his watch ‘They’re dead on time’ he said. He seemed mildly surprised at German punctuality, then returned to his breakfast”. The RAF has suffered severely during the preparatory air attacks, and the few remaining fighter aircraft are withdrawn the day before the assault. The main targets for the assault are, as expected, the three airfields. Despite the lack of air cover, at all three airfields the German crack parachute troops receive an entirely unexpectedly warm welcome, many being killed after their chutes open at 300 feet. By the end of the long day, the Germans have suffered severely, and are thinking that they will have to abandon the operation. But at Maleme they have gained a toehold and the next morning they capture the high ground overlooking the airfield. The counterattack is slow in coming and when it does it is half hearted. By mid-afternoon the Germans are landing transport aircraft on the runway, though it is still under fire. Communications are very poor as a result of the bombing, no-one having thought to ask for more radio sets during the build-up. The order to fall back from the airfield is given, and the battle has been lost as the Germans land a division of mountain-troops. This time the retreat is contested every step of the way, with both sides showing great courage. The New Zealanders seem to have recovered their renowned fighting spirit during the retreat, and the Greeks show great fortitude in holding up the advancing German troops to give the British time to cross the mountains. Perhaps most impressive of all, the local Cretan population, largely equipped courtesy of the weapons dropped to the German airborne troops that went astray, fought with all the fanaticism that their reputation as brigands might have led the Germans to expect. The strafing from the air is merciless, and must have been a major factor in the German victory, though the harassed troops on the ground probably failed to note that it slackened after 28th May when Hitler ordered that the aircraft be withdrawn to refit for the invasion of Russia (as BP learnt that day). The Allied mobile Y section proved its worth on several occasions. When the British had evacuated all they could from the island by 1st June the Allied force of 42,000 had suffered 3,500 casualties and 12,000 prisoners; the 22,000 Germans had suffered 5,700 casualties – more than they had lost in any previous campaign. At sea off Crete, the Royal Navy has totally destroyed the first convoy of sea-borne reinforcements, but is then forced to restrict itself to night working, as the casualties from air attack are horrific – 3 cruisers and 6 destroyers sunk and 17 ships damaged. It cannot have helped that the Germans were reading some of our naval codes. The two sides learnt contradictory lessons from the campaign. Hitler and the German High Command were horrified by the losses to some of their most highly trained and respected units; they never again relied on airborne forces alone in this way – though they did drop 900 airborne troops during their Ardennes Offensive in December 1944. The British and the US hurriedly started to build up their airborne forces, and used them on various occasions, such as the invasion of Sicily, on D-day, at Arnhem and on the crossing of the Rhine. (There is a close parallel for the fortunes of the British airborne landing across the Rhine to the German experience in Crete). It has been argued that the Crete operation caused Hitler to delay the launching of Barbarossa and so saved Moscow, though Crete was probably not the main reason for the postponement. But it certainly led to the cancellation of the airborne invasion of Malta. For BP the hard lesson was that excellent intelligence is not, by itself, enough. The Sinking of the Bismarck. The German surface raiders have caused severe shipping losses to the Allies. On the 8th May the German surface raider Pinguin, having sunk 28 merchant ships in ten months at sea, is sunk in the Pacific by HMS Cornwall. On 19th May the battleship Bismarck, accompanied by the cruiser Prinz Eugen, sails from Kiel for the North Atlantic. She and her sister ship, the Tirpitz, are Germany’s largest displacing 41,700 tons. The Admiralty had been expecting some such move, if only because Luftwaffe Enigma has disclosed unusual reconnaissance of ice conditions off Greenland. The Admiralty is warned on 20th May that two large German ships are at sea by the Norwegian Military Attaché in Stockholm, who had learnt it from Swedish sources. (The German secret service learnt that we had this information the next day, probably from decrypts of our signals). At this time Hut 8 at BP is just beginning to be able to read the German main naval Enigma key, Dolphin, but with delays of several days. On 21st May Enigma naval decrypts establish that the ships have embarked prize crews and appropriate charts for breaking into the Atlantic to raid the trade routes. Later that day, a photo-recce Spitfire manages to photograph them off Bergen where they have gone to fuel. On the evening of 22nd May a very brave RN pilot penetrates the low fog over Bergen and establishes they have left port. On the evening of the next day the destroyer HMS Suffolk makes contact by radar with the Bismarck in the Denmark Strait and continues to shadow the Bismarck when on 24th May she clashes with a Royal Navy task force, sinking with one salvo the ageing but still prestigious battleship HMS Hood, and then damaging HMS Prince of Wales. She, in her turn, is damaged by fire from the Prince of Wales and by a torpedo from an RN flight. The loss of HMS Hood is a bitter blow for the British public, especially as the cause seems to be the same weakness shown up in Royal Navy capital ships at the Battle of Jutland 25 years before, a flash-back down the ammunition hoist. (It has been suggested that, knowing the protective shield installed to prevent this would slow reloading, the Captain had taken the brave, if unwise, decision to keep the shaft open). HMS Suffolk finally loses contact with Bismarck in the early hours of the 25th. The difficult question for the Admiralty is where she is heading, and for several hours on the crucial 25th May C-in-C Home Fleet remains uncertain. Though Bismarck has made 22 signals, these are not read at BP; she is using a new capital-ship Enigma key, called Barracuda. Possibly misled by false intelligence planted by the Admiralty that the Home Fleet is still in Scapa Flow, she transmits three further signals on 25th. Harry Hinsley in Hut 4 at BP informs the Admiralty that he has spotted radio control of the Bismarck has passed from Wilhelmshaven to Paris, suggesting she is moving south. After some confusion in the Admiralty and on the part of C-in-C Home Fleet, during the evening of the 25th, based on Direction Finding on these three signals, the correct decision is reached that she is heading for Brest. Her fate now depends on whether her speed can be reduced sufficiently for her to be caught by the British battleships closing on her. On the evening of 26th in atrocious weather, and with little hope of landing back safely, torpedo aircraft from HMS Ark Royal secure two hits and jam her rudder. The capital ships now close, sinking her on 27th May. Hut 8 finally succeeds in breaking the related Dolphin traffic next day. By a remarkable chance, during the battle BP has learnt from a Luftwaffe signal that the Bismarck is heading for Brest. Their decrypt reaches the Admiralty on the early evening of 25th, but unknown to BP this is a few minutes after the decision has been made on the basis of the DF information. Though Hut 8 is unable to decypher the Bismarck signals, Hut 6 has read a signal in the Luftwaffe Enigma to a senior Luftwaffe Staff Officer who is in Athens preparing for the Crete invasion; by chance he has a son on the Bismarck and in answer to his enquiry the Luftwaffe HQ passes on the gist of one of the Bismarck signals giving the vital information. It would seem that BP believed that it was this signal that determined the fate of Bismarck, and used the story in training courses so it became well known. BP never broke the Barracuda key. The Bletchley Park Trust welcomes the preparation of these notes, but the authors are responsible for the statements and the views expressed. |
