From our archives...
February 1944 : Anxiety amongst the Planners
On his return to the UK, once General Montgomery had had time to study the plans for the ‘Operation Overlord’ invasion of Northern Europe in May 1944 prepared by a team under Lt.-Gen. F.E. Morgan, he soon decides that the landings will have to be on a wider front, putting more troops ashore in the first wave and so requiring more landing craft. His view that the ‘initial landings must be made on the widest possible front’ is endorsed by General Eisenhower and agreed by the joint Chiefs-of-Staff on the 8th February. But US Admiral King refuses to release more of the US landing craft, despite having at his disposal at this time 31,123 of which he directs that the majority should go for use in the Pacific, allocating only reluctantly 2,493 to Operation Overlord in the European theatre. Churchill had himself earlier argued for an increase in the first wave. He is keen to abandon the landings in the south of France, Operation Anvil planned for the same day as those in Normandy, with 1st May as the target date. He recognises that the diversion of some of the best fighting formations in Italy for these landings will make it improbable that a breakout into the Northern Italian plain can be achieved this year. But the Americans are adamant that the landings in the south of France must take place, seeing the Italian campaign as a sideshow. Churchill knows that there is no alternative to the landings in Normandy, but with all his bitter memories of Gallipoli and Dieppe, now reawakened by the German threat to the Anzio beachhead, he dreads ‘the prospect of bodies floating in the Channel’. This is a view no doubt privately shared by many in Whitehall. (When Morgan had taken office as chief planner back in March 1943 he had been greeted by Gen. Alan Brooke, the Chief of the Imperial General Staff, with the hardly reassuring comment ‘Well there it is, It won’t work but you must bloody well make it’). Probably influenced by Churchill, H.M. the King confides in his diary on 3rd February ‘The more one goes into it the more alarming it becomes’. At least there is no going back on the decision that the site of the landings must be in Normandy around the bay of Caen, now extended to the base of the Cotentin Peninsula. Despite the deception team’s numerous false messages positioning the coming landings anywhere and everywhere from the North of Norway down to the border of France with Spain, the planners know the only real choice has to be where there is good air cover from the UK and beaches suitable for landing supplies. These considerations limit the choice to the Pas de Calais and the Bay of Caen. It is Churchill himself who has provided the key to landing where there are no major ports available by recalling the plans he had had drawn up in the First World War for floating harbours to be towed to the landing sites.
The worries in Whitehall are accentuated by the threatened German ‘revenge weapons’. Though the U-boat menace seems defeated, it is known from decrypts that the Germans are developing air breathing ‘schnorchel’ submarines and novel pressure actuated mines. The threat to the armada off the beaches also extends to the German E-boats [which are to prove their potential at Studland Bay on 27th April]. The Luftwaffe is continuing to defend against air-raids with a ferocity that bodes ill for when they throw in the reserve that they must surely be gathering to defend the skies over the landing beaches. The Allied air offensive seems to be having little impact on aviation production, despite the same targets being attacked at night by the RAF and now by the USAAF on the following day. The offensive is bleeding the Luftwaffe white through the loss of irreplaceable experienced pilots, although the years of exaggerated kill claims make it difficult for Allied Commanders to recognise this. And over all looms the menace of the V-weapons. Intelligence on these weapons had been obtained from a special watch kept in Hut 3 at BP, from agents (including Colonel Bertrand known to BP from his work with the Poles), and from Photo Recce. The specification of the V1 is known in Whitehall from decrypts of the Baltic test stations reports. Some 170 launching sites had been detected, mainly in the Pas de Calais - Dieppe area aligned on London, but 10 in the Cherbourg area aligned on Portsmouth. The air attacks on the launching sites have postponed that missile offensive, but should it be directed to the crowded assembly harbours round the south coast it could cause devastation.
Anxiety amongst the Cryptographers. At BP it has long been recognised that the whole fabric of their code-breaking success could collapse if the Germans ever recognise that their codes and cyphers are being read, and so make simple but thorough improvements to their signals security. In 1943, BP has seen the steady consolidation of their success as the mastery of the Fish codes provides a partial alternative source of Intelligence to Enigma. It is known at BP that, after the capture of cypher machines and key sheets by the Allies in North Africa and Sicily, the German Services High Command has established an organisation, OKW/Chi, to inspect and tighten signals security. (The German Navy successfully resisted efforts by this body to inspect their signals security; they have a team of their own in the MND who monitor naval security and are about to carry out an enquiry into how the Allies had found out about three U-boat rendezvous locations in January & February 1944. It can hardly be said that the MND did so with an entirely open mind since they are asked to explain why reading of their signals ‘could not have taken place’!). Now there is ominous evidence of the tightening of signals security; the introduction of the variable reflector, UKD, poses a threat to BP’s mastery over Enigma, though February does not see the rapid spread of UKD that had been expected and dreaded. Now the introduction of the ‘P5 limitation’, preventing ‘depths’ by making the encryption dependent on the actual text, on virtually all the Fish network presents a threat to the breaking of these cyphers that is only being overcome by the triumph of the, now essential, machine approach. This is being fast developed in the Newmanry, helped by the timely arrival of the production Robinson machines and the entry into service of the first Colossus. With the use of land-lines by the German army in the area of the ‘Atlantic Wall’, few signals are being sent by radio, so the main military keys used in the Western France area cannot be broken, though some of the lesser keys are yielding as BP directs resources of men and machines to their breaking. Will the invasion lead to a tightening of security that may deprive BP of the Intelligence that the Allied forces so desperately need? This fragility of their all-important penetration of the enemy’s codes is recognised by all the senior staff at BP as they gear up to cope with the challenge that the invasion will pose. It is a very worrying time for those who are planning for the future at BP.
The Anzio Beachhead & Monte Cassino Battles. On 3rd February BP provided what the normally unemotional Official Historian described as ‘one of the most valuable decrypts of the whole war’. It was from a signal dated 28th January containing General Kesselring’s detailed plans for his counter-attack on the Anzio beachhead. A number of further decrypts followed, until on 15th February at 1345 hrs BP signalled that newly decrypted Luftwaffe intentions for the coming night heralded the start of the attack. It was the heaviest German counter-attack of the whole Italian campaign, involving 3 divisions and 270 tanks. The German spearheads might have succeeded in bisecting the beachhead, but the Allies had the immense benefit of a stream of decrypts enabling them to follow the battle from the enemy viewpoint, including warnings about the air, and motor-torpedo boat attacks against the shipping off the beachhead. (These motor-torpedo boat were from an Italian flotilla that had gone over to the Germans, as had been disclosed by Abwehr and Porpoise naval Enigma decrypts). When Kesselring called off this formidable thrust on the Anzio beachhead on 19th he reported that the Allies had correctly identified the main direction of his attack - as indeed they had from his own signals, so saving the beachhead from disaster. Ample decrypt warning was obtained of a further thrust on 29th February that made little progress and was finally abandoned on 1st March. [The near success of Kesselring’s counter-attack on the Anzio beachhead was to lead to mistaken tactics being employed by the Germans to counter the Allied landings in Normandy]. In the meantime the battle for the Monastery raged, with the failure of the New Zealanders’ attack over the Rapido on the night of 17th/ 18th, an attack designed to relieve the pressure on the beachhead. There were two decrypts on 19th February from Luftwaffe ‘Flyvos’ on the violent fighting for the railway station and Monastery Hill, but little of much help during this second battle for Monte Cassino. On 15th February the Monastery was demolished by Allied bombers in the belief that the Germans were using the building to observe the Allied movements, though there was no reliable Intelligence to support this. It has been said that an Army Y intercept by the 122nd S.R.I. Company suggested that a German ‘Abteilung’ (abbreviated Abt.) was in the Abbey, but that an Intelligence officer realised that this was a reference to the abbot (Abt) and not to the German battalion. It is now accepted that the Germans did not use the building until after the bombing. The destruction of the Monastery did not help the Maoris at Cassino station or the Gurkhas and Royal Sussex, who were attacking up the Snakeshead Ridge, for despite their outstanding heroism and heavy casualties little progress was made in the attacks of the 17th /19th February against the German paratroopers embedded in the rubble of the Monastery.
The War in the Air. Despite the opposition of various senior voices in Whitehall, who rightly doubted the efficacy of the area-bombing offensive, Bomber Command had opened the ‘Battle of Berlin’ on 18th November 1943. Their bomber losses rose appreciably in January (6% per raid) and again in February (7%), as German fighter strength over Germany continued to increase. The German night-fighter force has introduced new methods of interception that enable it to inflict increasing casualties, while circumventing the British counter-measures. They have raised the frequency of their early warning Freya radar chain, thus overcoming the effect of the British Mandrel jammers. They have overcome the effect of Window on the close-control radars by introducing a radio running commentary on the movements of the bombers, enabling their fighters to home on the bomber stream relying on their improved AI radars. Bomber Command reacted to this change of interception tactics by deceptive routing and diversionary raids, guided by the interception of these German running commentaries by the RAF Y station at Kingsdown and by the daily analysis of the enemy’s activities, known as BMPs, from the Air Section at BP. The RAF introduced their own running commentary, broadcast by perfect German speakers using the 600 kW transmitter ‘Aspidistra’, the ‘biggest in the world’. (On the night when the German first used a female speaker the RAF immediately used a WAAF, ready to take up the commentary). From early in December 1943, it became clear that further major changes in the German night-fighter system were making deception tactics increasingly ineffective. They introduced a new airborne interception radar set, SN2, immune to Window, and were inserting into the bomber streams their own specially equipped German aircraft. And they were now homing on the various radiations emitted by the bombers, such as from their identification equipment, IFF, and their navigation aids, H2S & Oboe. In December 1943, ADI (Sc), Dr R.V. Jones, had deduced that the Enigma decrypts of some unidentifiable plots were actually plots of Mk I Oboe, but it took a further six months before Bomber Command would fully accept that the Germans were capable of homing on their bombers’ high frequency transmissions, though they did introduce a centimetric Mk II Oboe. So after further very expensive raids on Berlin and Leipzig on 15th & 19th February ‘Bomber’ Harris is forced to change his force’s bombing tactics, diverting much of it to less well-defended areas. By the spring the belief that German morale would disintegrate before D-day has faded even in Bomber Command. Optimistic decrypts from the Japanese Embassy in Berlin, belittling the impact of the raids on Berlin, are part of the cause for this change of heart. On 2nd February BP has broken a new Enigma key, Roulette, used by the senior German police in occupied Europe and these decrypts add to the authority of the BP reports on the impact of the air offensive. At the beginning of 1944 the SIS had begun to circulate a regular new series of reports, frequently using the word ‘apathy’ to characterise the average German’s reaction to the raids.
Meanwhile in January 1944 the USAAF has resumed deep-penetration daylight raids, now accompanied by long-range Mustang fighters. The ‘Big Week’ raids of 19th-25th February, a series of precision attacks on aircraft industry targets during 19th-25th February, are considered a great success with the claimed shooting down of 600 fighters during the week. Though this claim is, as usual, a great exaggeration, it leads to the decision to choose targets and routes with the aim of destroying the enemy fighter force in direct combat. Luftwaffe Enigma decrypts from BP provide the most important source of Intelligence in planning these raids. [These new tactics were to lead to daylight air-supremacy by April].
Developments at BP. The new Enigma reflector, UKD, causes fewer problems for Hut 6 than had been expected. They break three new Luftwaffe keys, Leopard, Lama & Jaguar during the month. Colossus comes into service in February where it rapidly proves its worth, ‘immediately sending up the output to more than twice its previous level’ by finding the teeth positions set on some Fish machines. A new Fish link to Russia, Stickleback, is broken this month. At Eastcote the bombe girls suffer from firebombs, on 19th February, but the Wrens & the RAF lads soon had the fires under control.
The Codebooks buried on the Pacific Island. The Japanese attacks in the Arakan.
Warnings that the Germans were planning midget submarine attacks had come from Dolphin naval Enigma decrypts in December which showed that the Germans had salvaged British X-craft lost in the attack on the Tirpitz in Altenfiord. Porpoise and Luftwaffe Enigma decrypts gave good warning of the German human torpedo attacks on 20th April. (One of the triumphs of this false commentary was on the night when the Germans first introduced a female voice to distinguish their broadcast from the false one; the British had a female voice standing by!).
Impressions of Colossus at work. Quote from the end-of-war ‘Tunny’ Report: It is regretted that it is not possible to give an adequate account of the fascination of a Colossus at work: its sheer bulk and apparent complexity; the fantastic speed of thin paper tape round the glittering pulleys; the childish pleasure of not-not, span, print main heading and other gadgets; the wizardry of purely mechanical decoding letter by letter, (one novice thought that she was being hoaxed); the uncanny action of the typewriter in printing the correct scores without and beyond human aid; the stepping of display; periods of eager expectation culminating in the sudden appearance of the longed-for score; and the strange rhythms characterising every type of run: the stately break-in, the erratic short run, the regularity of wheel-breaking, the stolid rectangle interrupted by the wild leaps of carriage-return, the frantic chatter of a motor run, even the ludicrous frenzy of hosts of bogus scores. Perhaps some Tunny-breaking poet could do justice to this theme; but although an ode to Colossus and various fragments appeared, all seemed to have been composed in time of distress and despondency, and consist almost wholly of imprecation or commination’.
The Bletchley Park Trust welcomes the preparation of these notes, but the authors are responsible for the statements and the views expressed.
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"Does anybody know what the daily Intelligence reports about the Luftwaffe issued by Air Section at Bletchley Park, called BMPs, were like? What did BMP stand for? We know that they were immensely valued by the USAAF in their campaign against the Luftwaffe over Germany."