 | From our archives...May 1944 : The Approach to the Invasion: 1) The Land Battle1) The nervous leaders in London are not reassured by the steady stream of decrypts from BP showing that, though the Germans have not discovered for sure where the landings will be, their military commanders seem to have concluded that the blow will fall ‘in the Le-Havre - Cherbourg area’. They have not learnt the date or time but expect it to fall in a good weather spell in the next few weeks. But the good news is that the deception campaign seems to have worked to the extent that the Germans do believe the Allies have much greater forces at their disposal than is in fact the case, and expect the initial landings to be followed by further landings in the Pas de Calais. From patient work on the accumulated decrypts at BP, the Allies now know the location of virtually every German division in Northern France. The Fish link, Jellyfish, from the German High Command near Berlin to the C-in-C West, Von Rundstedt, at Paris provides detailed returns from a number of individual divisions, in particular the all-important Panzer armoured divisions, as well as strategic appreciations. On the 8th May a decrypt from C-in-C West discloses the unwelcome news that the Panzer Division Lehr has arrived in France and it is soon located at Chartres. Perhaps the most valuable decrypts provide, between 14th & 27th May, news from which it can be deduced that the powerful (20,000 strong) 21st Panzer division has moved up from Rennes to Caen - a dangerously short run to the eastern landing beaches. [This deduction was circulated to 21st Army Group but there is no indication that any attempt was made to strengthen the assault on this flank, where the all-important target of capturing Caen on the first day was now under threat]. Fish decrypts on 24th, 25th, and 27th May confirm that German reinforcements are now established in strength in the base of the Cotentin Peninsula round Le Haye-du-Puits, just where the US 82nd Airborne Division are going to be dropped to seize the roads into the Peninsula across the flooded area behind Utah beach. The US just has time to rearrange their landing zones and schedules [though on D-day the Division was spread over a wide region, partly due to the high wind, which had the benefit of thoroughly confusing the defence]. On the 13th May, the Joint Intelligence Committee warn that they now expect that some 60 German divisions will be available to oppose Overlord, a remarkably accurate prediction. After some reassessing of the size of these divisions, the JIC is able to reassure Churchill that this estimate falls just inside the upper threshold that had been set for calling off the landings. From decrypts of the Japanese Naval Attaché, following his tour of the defences in Northern France, the Allies know it is Rommel’s policy to destroy the assault near the coast, preferably on the beaches; but it is expected that the main counterattack will fall about a week after D-day. The worries in SHAEF are compounded by uncertainty about the timing of the Russian offensive, lest the Germans should be able to transfer divisions from there. For though Stalin has assured the Allies that he will time his summer offensive to prevent this, he does not give them any details [until 18th June - after the Russian Northern offensive had commenced on 10th June]. BP assist with decrypts of the German Y service Enigma key, Mustard, which make it clear the Germans are expecting a Russian attack but do not know the date. Decrypts from Japanese diplomatic signals, this time their Military Attaché in Vichy, have provided considerable details about the beach defences. During May small reconnaissance landings are made from midget submarines to investigate the under-water beach obstacles, which are causing much concern for those who now have to firmly fix the landing time in terms of the state of the tide. At least the good news of the success of the Allied attack in Italy seems to rule out German reinforcements coming from there. The priority the Germans are giving to these beach defences, and to preventing airborne landings is known from the decryption of C-in-C West’s urgent instruction of 13th May. The forest of posts that now sprouts from any possible landing field also caused much concern, for there is not much that could be done about these hazards [as the 6th Air-landing Brigade was to discover at St. Aubin to their cost on the evening of D-day]. 2) The Air Battle. As D-day approached, Hut 3 at BP looks carefully at the ample evidence on the locations, strength and preparedness of all Luftwaffe units that are likely to be engaged. They conclude the Luftwaffe has been husbanding its aircraft, but that only some 400 German fighters will be available for close support operations on D-day. They note the Luftwaffe’s serious lack of experienced aircrew. The Air Staff predict that the German bombers will be deployed by day and night to attack the assault forces before they are firmly established ashore, though they do not expect the Germans will be able to sustain this after the first 48 hours. The RAF seems confident of air domination, for the Intelligence from the many Luftwaffe decrypts enables them to be pretty certain that the Allied air assault has already gained the upper hand. By the end of May the RAF and the USAAF have attacked 34 main target airfields and 14 other operational bases during the intensified aerial campaign in France and Northern Europe. Hut 3 at BP becomes flooded with decrypts reporting on the damage. BP sends a copy of all such reports to Air Intelligence in the Air Ministry for the selection of further targets, but on 29th May BP is forced to announce that it can no longer afford the effort to summarise all of them for the Overlord Commands. The bitterly contested decision is taken to suspend the attacks on the airfields in favour of concentrating on the other aspects of the ‘Transportation Plan’ - the attacks on the roads, bridges, railways, radars, and communications; the Luftwaffe is a now seen as a lesser threat than the movement of the Panzer divisions. The attack on the railways was known to have seriously dislocated communications, but SHAEF concluded on 20th May that the attacks had so far ‘failed to restrict the enemy’s ability to move up reinforcements’. The authors of the plan in the Air Staff had argued that bridges were unsuitable targets, too expensive to attack successfully and too easy to repair - and the raids would cause many French civilian casualties. But the destruction of bridges in Italy had proved very successful during the current air offensive there. So Air Intelligence, after consulting BP, argued strongly that attacks on the bridges over the Seine and Loire should now be mounted. On 7th May the US Ninth Tactical Air force carried out spectacularly successful attacks on four Seine bridges. Unfortunately as decrypts show soon after, as a direct consequence the Luftwaffe Command in Northern France is now convinced the attack is going to fall in the Le Havre to Cherbourg area. So SHAEF had to decree that until the bridges over the Albert Canal had been destroyed there should be no further attacks on the bridges directly related to the D-day area. However, by D-day all 24 Seine bridges below Rouen had been made impassable, together with 12 elsewhere. 3) The Sea-borne Threat. The Germans were carrying out an extensive programme of laying mines both in coastal waters and further offshore in the months before the invasion. This programme was reconstructed in considerable detail, largely through the work of BP and the Admiralty’s Operational Intelligence Centre. Reading daily the main German Enigma naval keys (often in the twice enciphered Offizier Dolphin key) Naval Section at BP could reconstruct where the mines had been laid from German instructions to their own craft about the availability of swept channels. German torpedo boats had begun laying a barrage in the Seine Bay in February 1944, then in mid-March off Ouistreham (Sword beach), and then in April off the Cotentin Peninsula (in the ‘boat-lanes’ to Utah beach). An Offizier decrypt of 19th May contained details about a sortie from Cherbourg, which enabled British MTBs to intercept a force of German torpedo-boats, mine-sweepers and E-boats and sink two, damaging others. The resulting flood of encrypted navigation instructions for the damaged boats enabled the Operational Intelligence Centre to promulgate on 31st May the exact limits of the mine-free waters off the invasion beaches. It was naturally assumed that the Germans would use their U-boats against the landing fleets and follow-up convoys. In a most valuable series of decrypts on 19th & 20th May, obtained because the destruction of land-lines forced the Captain ‘U-boats West’ to use radio, he informed his HQ of his anti-invasion intentions. These provided BP with the plans in considerable detail, for the sailing of most of the Atlantic-based U-boats on D-day or D+1 to meet the invasion force. The Admiralty had been worried that there was a threat from new, small high-speed submersibles within the Channel, but just before D-day a decrypt from the Japanese Naval Mission in Berlin contained the most welcome reassurance that the Germans had not yet completed their experiments on the closed cycle engines for such boats. After the event, the Admiralty was criticised for exaggerating the threat still posed by Germany’s reduced capacity to respond, but no doubt many at sea in the huge invasion fleets would feel that such precaution was fully justified. [At BP the erection of aerials close to Block D and the installation of Y station Wrens in Hut 18 (the original Hut 8) was to prove fully justified in the rapid early warning it gave of German naval activity on D-day and during the following critical days]. 4) The Fuel Campaign. The German fuel supply had been recognised as an important target in the bombing campaign from the earliest days of the war, but that objective had been abandoned in the early months. The oil targets did not prove suitable in view of the operational limitations of night bombing. Once Germany had control of the huge Ploesti Rumanian oil fields and appeared likely to capture the Caucasian oil fields, she seemed to be too well supplied to make it a worth-while target. However, pressure for an attack on oil from the economic warfare experts was resumed in June 1943. US heavy bombers, flying from North Africa, attacked Ploesti in August in a raid that proved very expensive and was not thought to have done much damage, though it became known that it had seriously alarmed the Germans. On 5th March 1944 General Spaatz, commander of the USAAF, set out a ‘plan for the Bomber Offensive’ that included the oil targets as a primary objective. In the post-war testimony of BP, it is suggested that information about the effectiveness of the oil bombing campaign ‘may have been the outstanding service rendered by ‘Special Intelligence’ to the strategic air war in Europe’. Spaatz certainly had in mind that very likely the strained German fighter force would feel they had no choice but to come up to defend the oil targets. This choice of target was hotly disputed, [not least by Bomber Command, who were never enthusiastic over oil targets, and took little part in the offensive, even when directly ordered to do so in the autumn of 1944]. But Eisenhower recognised that the possibility of further weakening the Luftwaffe before D-day was an opportunity that could not be missed, and so gave Spaatz authority to make two attacks on oil targets to see if the Luftwaffe would give battle. The US 15th Air Fore, flying from the airfields now established round Foggia in southern Italy, made several attacks on Ploesti. On 12th May the US 8th Air force, flying from Norfolk, attacked synthetic oil targets using 800 bombers; the raids were strongly opposed with 46 bombers being lost. The USAAF claimed to have shot down nearly 200 fighters, though it seems the Germans actually lost only between 30 and 50, but even this was a vital aid to the forthcoming D-day battles. The raids were known from decrypts, probably Enigma and Japanese diplomatic traffic, to have done considerable damage and to have caused the German authorities very grave disquiet. So the US continued the oil attacks on 28th & 29th May. [On 8th June oil plants were given top priority for the US Strategic Bombers. From now on Germany was always short of fuel and, had Bomber Command joined in enthusiastically, might have crippled her earlier]. Fish. During the spring the Newmanry & Testery decrypt production work has concentrated on Bream traffic, since this is of direct value for the campaign that opens on 11th May in Italy. During March 1½ million letters of plain text were passed to Hut 3. (Bream operators at the Rome end - who move to near Florence when Rome falls on 4th June - have ‘bad habits’ that make it easier to read the Rome-to-Berlin rather than the Berlin-to-Rome link of the pair). All research effort is concentrated on the Jellyfish traffic from Berlin to the C-in-C West HQ at Paris, this being the crucial link for D-day, with success finally being achieved for the March wheel settings in early April. Jellyfish proves to employ the P5 device that prevents the use of depths, increasing the burden on the Newmanry. Despite this, during May the staff, working ‘under terrific pressure’, succeed in providing a steady flow of both Jellyfish and Bream decrypts. Some prove to be very valuable messages, for example position reports and returns from the Panzer divisions in Normandy and Italy which, once the proforma could be reconstructed and interpreted by Hut 3, provided vital Intelligence on matters like the number of serviceable tanks and fuel & ammunition supplies. A number of identical messages on Bream and Jellyfish have been found; ‘kisses’ but for Fish these are often long message repeats based on the use of the same auto-transmission tape from Berlin. [These will prove invaluable in June as cribs for Jellyfish after D-day, when the wheel patterns are changed every day on that vital link but not until August on Bream]. Gordon Welchman, now responsible for all mechanisation projects, has authorised the Dragon project to proceed; it will be used in the Testery to ‘drag’ a suitably crib word, say of 10 letters, at high speed through all positions of a long message. In May, cribs proposed by Sixta prove successful in wheel-breaking on Colossus. The plans for a new Block H are approved on 25th May to be ready for 17th September; thereafter it will be used to house Colossus machines No 5 to 11. [The seven Colossus in Block H were used for wheel-breaking, the four in Block F for wheel-setting]. As experience accumulates with Colossus, so the number of decrypts steadily rises. The Bletchley Park Trust welcomes the preparation of these notes, but the authors are responsible for the statements and the views expressed. |
