The Battle of Britain

by Richard Overy

Technical problems like these may seem trivial when set against the sombre prospect of invasion, but they were the necessary components of a complex system of ‘command and control’ which gave Fighter Command a real striking power and operational flexibility. The heart of the system lay at Command headquarters at Bentley Priory in Stanmore, on the outskirts of London. It was here, in the Filter Room, that information on incoming aircraft was relayed by landline from all the radar stations around the coast. The plots were laid out on a large map table, and once the aircraft track was clearly established, this information was relayed in turn to the Group Headquarters and the individual Sector Stations (airfields). Additional intelligence was supplied by the Observer Corps whose members plotted enemy aircraft visually once they had crossed the coast. This information went first to an Observer Corps Centre, and then straight to Sector Stations and Group Headquarters. Group commanders then had to decide which of their sectors to activate, while Sector Station commanders were responsible for deciding which of their squadrons should fly on a particular operation. Once airborne, aircraft were controlled by Radio-Telephony Direction-Finding (R/T-D/F). The whole process was supposed to take minutes only. Without speed and clear instructions the system was pointless.17

  The entire structure of communication was dependent on early warning and continuous observation. The heart of the system was the Radio Direction Finding (RDF) apparatus, better known by the acronym RADAR (Radio Detection and Ranging). The technology was first developed in 1935 when it was demonstrated that aircraft reflected back to ground short-wave radio pulses, which could be captured on a cathode ray tube. By 1939 there were 21 so-called Chain Home radar stations circling Britain’s coastline, theoretically capable of detecting the height and range of approaching aircraft up to 200 miles distant. Average range was only 80 miles, but adequate for the German air threat across the Channel. The radar stations could not detect aircraft flying below 1,000 feet, and a second system of Chain Home Low stations was established after the outbreak of war to detect low-flying aircraft and coastal shipping. These stations had a range of only 30 miles and could not predict height, though that mattered less at such low altitudes.

  Radar could not yet work inland. It had to be supplemented by the Observer Corps, formally founded in 1929, and commanded in 1940 by Air Commodore A. D. Warrington-Morris. It was staffed by volunteers across the country who largely trained themselves in aircraft recognition and methods of height estimation. On the outbreak of war there were 30,000 observers and 1,000 observation posts, each armed with a grid map, a height estimator, telephone, coloured map markers and the means to make tea. Posts were manned continuously; the system worked well in fine weather, but was defeated by low cloud cover and rain. Height estimation was difficult and often inaccurate. Group headquarters found that numerous Observer Corps plots cluttered up the map tables with a surfeit of less reliable information.18

  Radar, too, was by no means infallible. Height readings could be thousands of feet out; the time-lag was at times too long between sighting enemy aircraft and scrambling fighters to meet them (it took a minimum of four minutes for the squadrons to receive radar warning, but only six minutes for enemy aircraft to cross the Channel); radar equipment was continuously upgraded, which left some stations inoperable for brief periods while new technology was installed. By the time of the battle, secret intelligence was being supplied from decrypts of German Air Force ‘Enigma’ traffic, but although this was useful in building up a clearer picture of the German order of battle, it was less useful in giving information quickly enough on the scale and destination of major raids. This was not the case with low-level radio interception, whose role has generally been neglected. The RAF wireless interception station at Cheadle took advantage of the slack radio discipline displayed by German aircrew to supply a regular diet of accurate reports on range, destination and origin of aircraft which was relayed directly to Command headquarters as well as Group and Sector commanders. The net effect of all these different sources of intelligence was to create a web of information that gave Fighter Command an essential counter to the element of surprise enjoyed by an enemy who could pick and choose when and where to attack.19

  Fighter defence was supplemented by a network of anti-aircraft guns and barrage balloons. Anti-Aircraft Command was established only in April 1939. Headed by Lieutenant-General Sir Frederick Pile, it was integrated with Fighter Command to provide a unitary defence network. A crash production programme for anti-aircraft artillery was pushed through, but could not make up for severe deficiencies. By June 1940 there were 1,204 heavy and 581 light anti-aircraft guns to cover the entire country, far short of the planned 2,232 heavy and 1,860 light guns. The batteries were activated, like the fighter stations, from Fighter Command headquarters. The country was divided into 130 warning districts, based on the layout of the national telephone system. Three telephone operators at headquarters kept in continuous contact with trunk-exchanges in London, Liverpool and Glasgow. When enemy aircraft were 20 miles distant, a ‘yellow’ warning was sent to the endangered districts to place emergency services on alert. Five minutes later a ‘red’ alert would follow and air-raid sirens would start up, followed shortly by the anti-aircraft barrage. ‘Green’ indicated that the aircraft had passed and signalled the all-clear. It was a system that worked almost too well. During the summer of 1940 whole areas of the country were sent scurrying into air-raid shelters at the distant approach of a handful of aircraft. The disruption to normal work-time brought the government to the point of abandoning air-raid warning altogether. In June 1940 the Minister of Information, Duff Cooper, suggested that people should accustom themselves ‘to receiving no warnings when only a few aircraft were in the neighbourhood, even if these aircraft dropped bombs’, but the Cabinet sensibly opted to retain some element of warning.20

  The air defence system was set up to counter an enemy bombing offensive and to ameliorate its effects on the bombed population. In the summer of 1940 it had to be adjusted to the threat of invasion. The two operations were by no means the same. Invasion presented Fighter Command with a range of new responsibilities, including close collaboration with Bomber Command, whose aircraft had to be protected as they pounded the invasion beaches. Provisional plans were considered as early as October 1939 when it was agreed to supply the army with two squadrons of Blenheims and one army co-operation squadron to repel an invasion force. The assumption underlying this feeble gesture was that no invasion could be attempted until Fighter Command had been neutralized, and that the real battle would be fought in the skies over southern England long before invasion could be undertaken.21

  By the summer of 1940 invasion was a much more realistic threat. Fighter Command was instructed by the commander-in-chief of Home Forces, General Sir Alan Brooke, to prevent the German Air Force from achieving air superiority and to protect airfields and other vital military targets. At the same time fighters were expected to attack, in order of priority, enemy transport aircraft bringing in men and supplies, enemy dive-bombers, high-flying reconnaissance aircraft and enemy fighters attacking RAF bombers over the invasion area. This dizzy list was enlarged in late summer by additional requirements to protect naval vessels and bases and to attack enemy barges and sea transports with cannon-armed fighters. Bomber Command, meanwhile, was asked to attack ports of embarkation by night. During invasion, bombers were needed immediately over the invasion beaches, where it was hoped invasion could be nipped in the bud in no more than forty-eight hours of ‘utmost physical and mental effort’.22

  Much thought was given to subterfuge. In the October directive it had been assumed that Germany might try to seize airfields using small units of tough airborne troops.23 German success in capturing the fortress of Liège in May 1940 gave real substance to the fear, and priority was given to strengthening airfield defence. The results were often lamentable. Two separate inspections were undertaken by army commanders. They found some anti-aircraft guns placed on the roofs of vulnerable buildings,
others scarcely concealed, and many incapable of either seeing or engaging low-flying aircraft. Many stations had neither barbed wire nor pill-boxes. It had been decided that RAF ground personnel should not be armed, so that airfields had to rely on local army units, which would be expected to arrive only after a delay of one to two hours, and in force in only four hours. In August, RAF airfield staff were given arms again, but were not yet properly trained in their use.24 Reports showed that when enemy aircraft occasionally landed on British airfields, they were able to take off again unmolested.

  There were also fears that German forces would use poison gas to achieve swift mastery of key front-line airfields. To this threat the only answer was deemed to be retaliation in kind. The Air Ministry sent stores of gas bombs (chiefly mustard gas) to airfields, where they were prepared ready for use at three hours’ notice. The Air Staff preferred the idea of using gas against soldiers on the invasion beaches to be sure of containing the threat at once, but Churchill and the chiefs of staff instructed the Air Ministry in late September to plan for gas attacks on the German civilian population in case gas was used by the Germans in the early stages of invasion.25 Gas attacks were also considered in the special case of a German surprise attack on Ireland, a fantasy that still lived on in Whitehall circles throughout the summer and autumn of 1940. In late June the Air Staff directed the small air force stationed in Northern Ireland to prepare for an attack on German troops ‘and I.R.A. irregulars co-operating with them’. Bomber aircraft were to fly from the mainland bringing either gas or high-explosive bombs. All air crew were asked to exercise ‘particular discretion’ when attacking targets south of the border ‘which may cause loss of life to Irish civilians’.26 This prospect must have seemed a peculiarly daunting one for the force of 12 fighters and 20 light bombers available in Northern Ireland to repel the hitherto unstoppable Wehrmacht. In the end, none of these fears materialized, neither the gas and airborne assault, nor the invasion of Ireland. German military leaders recognized that the preliminary to any land operation was the elimination of the enemy air force, and made their plans accordingly. Victory over France transformed the prospects for a successful air campaign for it allowed the German Air Force to fly from any point on the European coastline from Norway to Brittany. The critical factor for the German side was the short range of the Messerschmitt Me 109 single-engined fighter. Flying from Germany, it would have had hardly any time for combat over southern England; even flying from bases in northern France, the Me 109 could only reach as far as London. When engaged in heavy combat, which used up fuel more rapidly, London was difficult to reach. Some efforts were made to extend fighter range. A disposable drop fuel tank made of moulded plywood was developed before the war, but it was prone to leak and easy to ignite, and was not used. In the summer of 1940 experiments were conducted in towing fighter aircraft for the first part of their flight, but this tactic was also abandoned.27 Prior to invasion, the German Air Force could only contest air superiority across an arc stretched over Kent, Sussex and Surrey.

  The air forces that faced Fighter Command were nevertheless stretched out around the northern European littoral. Air Fleet 5 was stationed in Norway, and could only attack with long-range aircraft. Preliminary skirmishes by day in August showed that these aircraft would take unacceptably high losses both from enemy action and the long over-sea flight, and Air Fleet 5 took no further part in the battle. The territory covered by Air Fleet 2 stretched from northern Germany, through Belgium and the Netherlands as far as Le Havre in occupied France. Fighter squadrons were clustered in and around the Pas de Calais, close to their targets. To the west lay Air Fleet 3, which had a much larger complement of bombers and dive-bombers for the attack on coastal areas and naval targets.

  Air Fleets 2 and 3 were led by two middle-aged Bavarians, the cream of the new generation of air force commanders appointed in 1935 when the German Air Force was refounded. Air Fleet 2 was led by Field Marshal Albert Kesselring, recently promoted for his contribution to the defeat of France. He is best remembered for his stubborn and occasionally brutal defence of northern Italy against Anglo-American armies later in the war, when he once again reverted to his original career as an army officer. Though lacking air experience, he proved an able organizer, with a genuine authority. His geniality made him a popular leader. Kesselring’s fellow commander in charge of Air Fleet 3 was Field Marshal Hugo Sperrle, who led the notorious German Condor Legion during the Spanish Civil War. He, too, was a career army officer, with limited flying experience from the First World War. Sperrle, like Kesselring, was energetic and popular, his corpulence a match for that of his plump commander-in-chief. Though neither had the long air force experience of Newall or Dowding, they brought with them all the qualities of organizational and operational understanding that set the German army apart in the early years of the war.

  The task the two commanders faced in the summer of 1940 was one poorly anticipated in the 1930s. The German Air Force had to adjust in short measure from the role of close army support to a campaign of independent air operations against a well-armed air enemy. This change brought a host of practical problems. A whole network of air bases had to be established across northern France. Some existing French air stations could be used, but even these needed to be supplied with stocks of food, oil and spare parts to function effectively. The repair organization, vital for maintaining high levels of serviceability, was more difficult to improvise locally, and many damaged aircraft had to make their way by road and rail back to the Reich for repairs. In order to cope with the new conditions, German fighter forces were gathered into separate operational commands, rather on the lines of the British Group. However, they lacked two significant advantages enjoyed by the RAF: they had no way of tracking where the enemy was, and there was no way of controlling the whole fighter force from the ground once it was airborne.28

  The German Air Force also operated throughout the coming battle with low levels of reserves. This was largely a consequence of the poor performance of German aircraft production. Even though Hitler granted special priority in June to the air and naval armaments needed to subdue Britain, the supply of aircraft remained sluggish throughout 1940. Pre-war planning had anticipated a doubling of aircraft production in the first year of war to reach more than 20,000, but these targets were regularly scaled down during 1939 to match factory output. Plan 15, in September 1939, and Plan 16, drawn up only two months later, both reduced planned production in 1940 to little more than 11,000. A new plan was drafted in July 1940, but it offered even lower output for the second half of the year. Some effort was made to give fighter production greater priority, but during 1940 only 1,870 single-engined fighters were produced against a planned output of 2,412.29 This was less than half the British figure. During the summer and autumn of 1940, output of the Me 109 reached 164 in June, 220 in July, 173 in August and 218 in September, a grand total of 775 against the 1,900 fighters produced in Britain.30

  There were many causes for the deficiency but complacency was not one of them. Goering pressured and bullied the aircraft industry every bit as much as Beaver-brook. Nor were the resources lacking. The German aviation industry had access to the most advanced aeronautical technology in the world and enjoyed larger resources of machinery, raw materials and manpower than the British. The answer must be sought elsewhere. The leading culprit was the head of air force procurement, Colonel Ernst Udet. If ever there was a square peg in a round hole, it was Udet. A former First World War fighter ace, he became a well-known stuntman and film-star in the 1920s, and was a noted cartoonist. He gravitated to Goering’s social circle, and was chosen out of the blue to head the air force technical office in 1936, partly because of his popular reputation, partly because Goering wanted a subordinate who posed no threat to his authority. Udet was a ladies’ man and bon viveur, a daring test pilot and man of action, but he was also a political lightweight who found himself utterly out of his depth in a senior bureaucratic post in which long experience and wi
de technical knowledge were irreplaceable assets. He was manipulated and misled by the businessmen and officials who surrounded him. Later, in 1941, in desperation at his impossible position, he committed suicide, scrawling on the wall of his apartment before he died that Goering had betrayed him to ‘Jews’ in the Air Ministry.31 His place was taken too late by Field Marshal Erhard Milch, state secretary in the Air Ministry and a former director of Lufthansa, who had been sidelined by Goering in the late 1930s because he threatened to be too competent.

  The German Air Force was still a formidable enemy in 1940. It was armed with some of the best combat aircraft then available. The high standard of production and the technical complexity of German aircraft provide at least part of the explanation why Udet found it so difficult to raise the production threshold quickly. In the Messerschmitt Me 109 (also known as the Bf (Bayerische Flugzeugwerke) 109) Germany possessed arguably the world’s best all-round fighter aircraft. The bulk of the force that fought in the battle bore the suffixes E-1 and E-3, variants with improved engine performance introduced during the course of 1939 and 1940. The Me 109E-1 had a top speed of 334 mph at 19,000 feet, and a ceiling of 34,000 feet. It was armed with two 20 mm cannon and two 7.9 mm machine-guns. The cannon provided a less rapid rate of fire than British fighter weapons, but the explosive shells were more effective. In the summer, armour was added to give the pilot enhanced protection. The Me 109E could be out-turned by both the Hurricane and the Spitfire (though whether this was due to the fact that British aircraft used higher-octane aviation fuel remains open to debate); at heights above 20,000 feet, however, the performance gap between the two sides widened considerably in the Messerschmitt’s favour. Because the German fighter’s DB 601 engine had a hydraulic supercharger, which allowed variation of speed with altitude, the Me 109 could fight much more robustly at high altitudes than it could at the lower levels flown by German bombers. If the Battle of Britain had been fought at 30,000 feet, the RAF would have lost it.32