Both Germany and Britain were hindered by their lack of military or political intelligence throughout the summer of 1940. A central explanation for Hitler’s ill-judged speech at the Reichstag was that the Germans had no inside knowledge of the British political scene, and were still relying on the preconceived notion of Churchill as an unpopular plutocrat.
Although the Nazis had cracked some of the Admiralty radio codes, thereby gaining useful information about ship movements, they knew little about the army, the RAF or the strength of Britain’s defences. In fact, Hitler once bewailed Germany’s ignorance about its enemy, given that she lay only 21 miles away from occupied territory: ‘It seems incredible that we do not have a single informant in Great Britain.’ British military leaders complained just as bitterly about being kept in the dark, largely because the German occupation had destroyed the Allies’ networks of agents across Western Europe and resistance cells had not yet been established.
But Britain did have one advantage over the Germans: the work of the government’s Code and Cipher School at Bletchley Park, where the pioneering use of semi-electronic computers was beginning to yield results in decrypting the latest codes employed by the German military on their ferociously complex Enigma machines.
A crucial breakthrough came on 22 May 1940 when the decoders succeeded in unlocking the traffic between Luftwaffe operational units and Goering’s headquarters. The intelligence from the Enigma decrypts was known as Ultra and was regarded as so important that it was circulated to only a handful of military and political leaders, including the Chiefs of Staff, Churchill and Ismay.
The Ultra decrypts were personally taken to the prime minister each day by Sir Stewart Menzies, the head of MI6, another indicator of their importance, and were carried in a special buff-coloured box, for which Churchill alone in Downing Street had the key. Indeed, the existence of Ultra was so secret that it was kept from the public until the 1970s, when the retired senior intelligence officer Group Captain Frederick Winterbotham, who was in charge of the Ultra decrypts, published his memoirs. Churchill himself approvingly described the Bletchley Park staff as ‘the geese that laid the golden eggs and never cackled’.
In late June 1940, the Bletchley listeners were able to provide one intriguing detail that appeared to indicate that the Germans were planning major landings on the British Isles. The message ran: ‘on 20 June, a request from Flakcorps 1 (anti-aircraft corps) for the following maps to be delivered, among others, immediately to their HQ: i) 800 copies, England and Ireland, scale 1/100,000 and 1/300,000; ii) 300 copies, France and England, scale 1/1,000,000’.
Perhaps even more valuable was an analysis of the decrypts in early July by air intelligence, which seemed to show that German bomber strength was much lower than expected. Instead of the 2,500 front-line bombers previously thought to be held by the Luftwaffe, the estimated number was now believed to be 1,250, or half that. Describing the figures as ‘heaven-sent’, the air staff said that the forthcoming German aerial offensive could be viewed ‘much more confidently than was possible a month ago’. Yet over the coming months, the Luftwaffe traffic did not yield as much solid information as the British government had initially hoped when the Luftwaffe code was broken.
In fact, Ultra was of limited benefit in mid-1940, for two reasons. One was that the German military, including the Luftwaffe staff, tended to use secure telephone landlines rather than the radio throughout their occupied territory. Another was that Goering, puffed up with arrogance, was completely detached from the invasion planning process and had no interest in cooperating with the other commanders, as he showed by his regular non-attendance at conferences.
Given Ultra’s limitations in July, the British therefore still had to turn to other sources of intelligence, whose varied quality gave rise to constant empty rumours and false alarms. Indeed, after submitting a report stating that ‘a fairly reliable source gives 5 July as the date for invasion’, MI14, the German section of British Intelligence, admitted candidly, ‘we doubt if any source open to us can be in possession of such accurate information.’ Nevertheless, the defence authorities had a duty to consider every piece of data that might shed light on the invasion plans. At the end of June, for instance, Lord Halifax circulated a report from Polish sources in the Turkish capital Ankara, warning that the invasion would be mounted in the second week of July. Partly as a result of this report, speculation grew about the imminence of an attack on 8 July, although such talk was never taken too seriously. ‘This is the zero hour for Hitler’s invasion of England – the actual date favoured by tipsters being about 8 July,’ Sir Alexander Cadogan recorded drily.
When that day passed without incident, Thursday 11 July became the rumoured new date of destiny. John Colville wrote in his diary with a hint of cynicism, ‘The invasion and great attack is now said to be due on Thursday.’7 When the day came and the Channel crossing similarly failed to materialise, he noted that new intelligence pointed to Norway as the possible base for a German assault.
In the same vein, on 10 July, another intelligence report to the committee stated that ‘training for combined operations is being carried out in the Baltic’, and, even more disturbingly, that ‘Germany intends to use poison gas in the attack on Great Britain.’ But two days later, in a further sign of how poor the intelligence was, another report admitted that the sudden, recent focus on Scandinavia might have been misleading.
Other information sent to the defence authorities pointed elsewhere. Admiral Drax, the commander of the Nore, circulated to the Chiefs of Staff an ominous rumour he had heard from three Dutch army officers who had escaped from occupied Holland. According to this Dutch trio:
The German preparations in Holland for the invasion of England are obvious and the German slogan is ‘London on 15th July. Every craft that can be made capable of making the crossing is expected to start on 11 July, and one and a half million men are being transported in various small craft. A very large number of parachute troops are in Holland and are continually practising. Large quantities of troops are to be airborne and special underground starting places complete with runways have been constructed. Planes have been specially constructed to land in small places, i.e. – the size of a football ground. The plan for invasion is the launching of a parachutist attack which is intended to withdraw the troops from the coast, thus facilitating the task of the first landing parties which will come from all ports from Norway to Belgium. After the first parties have secured a footing, the main landing force will arrive in larger ships. The Germans estimate there will be a total invasion force of three-and-a-half to four million.
The absurd scale of this supposed operation, as big as Barbarossa if it had been mounted, rightly undermined the credibility of the rumour.
Amidst this miasma of false trails, exaggeration and gossip, there was one unintentionally comedic result. The prime minister decreed that all the intelligence reports and Bletchley decrypts about the potential invasion should be classified under the code name Operation Smith, since the British knew nothing about the German title, Operation Sea Lion. Indeed, it was not until late September that Bletchley discovered that the Germans’ invasion plan was called Seelöwe. However, Churchill’s choice of name was unfortunate, as the government scientist R.V. Jones later recounted:
It turned out that the War Office had its own ‘Operation Smith’ that was concerned with the invasion. It was the code name for the movement of one of its minor administrative branches from its current headquarters in Tetbury to some place further north if the Germans should have invaded and posed a threat to south Gloucestershire. The result was that when the Bletchley teleprints were received in the War Office, duly headed according to the Prime Minister’s instruction, they were immediately sent to a Colonel in Gloucestershire, who no doubt impressed by the service that the War Office was providing but realizing that the material was too secret for general circulation, locked them in his safe and told nobody.
For all the conflicting advice from the continent, the government had to prepare for the worst eventuality. As Churchill said in his radio broadcast of 14 July, perhaps the invasion might ‘never come’ but he knew Britain could not rely on such blind optimism. Everything possible had to be done to secure the country’s defences, since it was in Germany’s essential interest to conquer her last remaining foe in Western Europe. Ironside wrote in his diary: ‘This looks like the decisive month’ for ‘there can be no doubt that vast preparations in the way of air and sea invasion are being made’.
Always fascinated by military strategy, the prime minister himself was considering the nature of the invasion threat and the effectiveness of Britain’s resources. In a paper of 9 July, he struck a dismissive note about Germany’s chances of launching a successful assault, particularly because of the strength of the Royal Navy. ‘I find it very difficult to visualize the kind of invasion all along the coast by troops carried in small craft and even in boats. I have not seen any serious evidence of this class of craft being assembled and except in very narrow waters, it would be a most hazardous and even suicidal operation to commit a large army to the accidents of the sea in the teeth of our very numerous patrolling forces.’ With remarkable boldness he expressed his disbelief that ‘the south coast is in serious danger at the present time’, because ‘no great mass of shipping exists in the French ports’, with the Dover mine barrage acting as a deterrent.
Partly in response to Churchill’s paper, the First Sea Lord Sir Dudley Pound produced a more circumspect analysis, setting out his view of the German threat. On the seas, it was true that Britain enjoyed naval superiority, but this could be countered by air power. Following the launch of an invasion, ‘large numbers of German air forces will be concentrated on our warships in the narrow seas in an endeavour to prevent them operating against invading forces’. Contrary to Churchill’s positive view, he said that it would ‘never be possible for the Admiralty to guarantee’ that German landings could not take place in the south, partly because of advances in naval technology. ‘In the hundred years since invasion of this country was last seriously talked about the Channel and North Sea have become very much narrower because of the greatly increased speed of the craft that might be employed and the crossing of these waters by large numbers of high speed, small boats is now a practicable matter. The whole crossing can now be undertaken in many places in the dark hours.’
Continuing in this pessimistic vein, Pound wrote that the most likely launch points for such barks were between Calais and the Netherlands. ‘The enemy may well have prepared a considerable number of these fast craft and it is not impossible that, say, 400 of these vessels, each capable of holding 40 men, may be in readiness.’ If these fast vessels were to travel across to England at 30 knots, ‘the likelihood of our destroyers being able to get to the spot in time to take any considerable toll is not great. The coastal patrols themselves, being slow and of weak armament, could not be expected to stop more than 20 per cent of such a force.’ Taking account of potential embarkation from Nazi-occupied Denmark and Norway, as well as from ports in Germany, Pound believed it was probable that ‘a total of some 100,000 men might reach these shores without being sufficiently intercepted by naval forces.’ It would be difficult for the invader to maintain supply lines, but, on the other hand, ‘he could make a quick rush on London, living off the country as he went, and force our Government to capitulate’.
On seeing Pound’s paper, Churchill struck an emollient tone. Rather than dismiss the First Sea Lord’s arguments, in his reply of 15 July sent to the Chiefs of Staff, he said he was certain ‘that the Admiralty will in fact be better than their word, and that the invaders’ losses in transit would further reduce the scale of the attack’. However, he urged the chiefs to review their invasion plans and make sure that they had the land forces to repel a German attack of 100,000 men, which in practice meant at least 200,000 troops in the home defences.
Churchill’s demand to the chiefs for a minimum defence force of 200,000 was in fact rather modest in the context of a growing strength at home. Since the dark days of May, when the country seemed hopelessly ill equipped to cope with an assault, Britain’s security had radically improved. On every front, the nation was becoming better prepared. Fighter Command, having proved its capabilities over Dunkirk, was rapidly expanding its fleet. Between 29 June and 2 August, 488 Hurricanes and Spitfires came out of the factories. In early May, Fighter Command had an establishment of little more than 600 aircraft. By mid-July the figure had reached over 900, with Hurricanes and Spitfires making up the vast majority of planes. In addition, the radar stations and the Royal Observer Corps, now both fully operational, gave the RAF an invaluable warning system about hostile Luftwaffe activity; while the technically minded head of Fighter Command, Sir Hugh Dowding, had devised a highly efficient command structure for processing information about enemy movements, which meant that fighter resources could be directed to where they were needed most.
Similarly, the Royal Navy was an increasingly strong obstacle against invasion, with the coastal fleet, gun batteries and mines all being reinforced. It was the same reassuring story with the coastguard, which, having been taken by the Admiralty from the Board of Trade, had been ‘doubled in strength and armed, so that the maximum patrol beat between posts was only half an hour,’ reported Pound to a meeting of government ministers on 15 July. As regards the main Home Fleet, Pound’s news was equally heartening. There were now, he said, at least fifty destroyers, thirteen cruisers and nineteen corvettes in home waters.