The Battle of Britain - Britain's Defences, 1940

Posted on Monday 9th July 2012

Extracted from Battle of Britain - Airfields of 11 Group by Peter Jacobs and reproduced by permission of Pen and Sword Books Ltd.

During the battle Fighter Command was divided into four groups, each with an Air Vice-Marshal as its Air Officer Commanding (AOC). Each group was split into a number of sectors, which, established geographically, eased the command and control of the bases and fighter squadrons within each group.

The responsibility of No 11 Group was the protection of London and the south-east of England, which meant that it was in the forefront of the battle. To the west of No 11 Group was the newly formed No 10 Group, which had the responsibility of protecting the area from mid-Hampshire to the West Country, the industrial part of South Wales and as far north as the southern Midlands. No 12 Group was responsible for the Midlands, the rest of Wales, and the area northwards to a line running across the country from the Lancaster area to just north of Flamborough Head. No 13 Group covered everything else in the north of England and Scotland. Incidentally, at the end of the Battle of Britain period, the number of groups was increased to six, with No 9 Group covering the north-west of England and No 14 Group covering the far north of Scotland. Fighter Command’s area of responsibility was essentially overland but extended to five miles off the coast, with Coastal Command being responsible for the area beyond.

In command of No 11 Group was Air Vice-Marshal Keith Park. Born in New Zealand, Keith Rodney Park had served in the Royal Flying Corps during the First World War and as Dowding’s Senior Staff Officer in Fighter Command before he was appointed AOC. The group’s headquarters was at Uxbridge in Middlesex, about 20 miles to the west of central London, and its responsibility was to protect the south-east of England, which included the area from Harwich south across the Thames estuary to Dover, then westwards along the south coast just beyond Southampton, and northwards to the north-west of London.

Once France had fallen, one of the major problems facing the group was the exposure of its airfields to air attack. With the Luftwaffe’s occupation of forward bases in northern France, all of No 11 Group’s airfields were within comfortable range of the German bombers. In June 1940 the Air Staff requested more airfields. For No 11 Group this meant finding at least one suitable site close to all its recognized airfields, which could either be used as an emergency landing ground or, if necessary, as a base from which operations could be carried out. Initially, the state of the site was not considered overly important. As long as the grass area was long enough and suitably flat for fighters to operate from, the rest could be developed if necessary. Any development, however, would be limited to runway preparation and the provision of basic facilities to ensure that the fighters could be refuelled and rearmed; living and maintenance had to be managed as best as possible.

At the beginning of July 1940 there were eight sector airfields in No 11 Group, which formed a formidable line of defence from the north-east of London to the south-west of England. The airfields were: North Weald (Essex), Hornchurch (east of central London), Biggin Hill (Kent), Kenley (Surrey), Tangmere (West Sussex), Middle Wallop (Hampshire), Northolt (west of central London) and Filton (Bristol). Within days of the battle opening the number of sectors was reduced

The main battle area.

The sector airfields of No 11 Group that did not have them rapidly gained satellite airfields, advanced landing grounds or relief landing grounds. Although these often began as simply large grass areas, many were soon transformed into airfields with facilities for the permanent accommodation of either small detachments of aircraft and personnel or complete squadrons.

Every effort was made to confuse the Germans, including camouflaging airfields and constructing decoys complete with wooden aircraft and dummy flare paths. Examples of these during the Battle of Britain were at Barnet, to the north of London, where a dummy airfield was created on the local golf course, and at Lullingstone to the north-east of Biggin Hill. Camouflage, in particular, was given a high priority and various techniques were used to break up the shape of aircraft hangars, key buildings and the airfield itself. Those that had hard runways and aircraft aprons were treated so that the hard surfaces were ‘textured’ to prevent them from standing out when seen from a bomber at medium altitude. There were also examples of local innovation. For example, an airfield surrounded by housing was often camouflaged so that hangars and technical buildings looked like houses. The idea was to make the airfield blend in with the surroundings as much as possible. It was, of course, fully accepted that to try and hide an airfield and prevent an attack by day in good weather conditions was difficult, but the idea was simply to cause doubt in the minds of the bomber crew about the location, size and aspect of the target. This could all result in a vital delay in a bomber releasing its bomb load and therefore prevent it from hitting its target. Although the camouflage of airfields continued until about 1943, the need for decoy airfields was rather more short-term, as by the end of the Battle of Britain the Luftwaffe had taken to bombing at night rather than by day.

The Aircraft

As No 11 Group was in the forefront of Britain’s defence, it had more squadrons then any other group. When the Battle of Britain opened, it had approximately 350 aircraft and twenty-two squadrons: thirteen equipped with Hurricanes, five with Spitfires, three with Blenheims and one with Defiants.

The Hawker Hurricane was designed by Sydney Camm and first flew in November 1935. The first aircraft entered service at the end of 1937 and by early 1940 more than 600 were in service with the RAF. The Hurricane I was powered by a Rolls-Royce Merlin engine and armed with eight 0.303 in Browning machine guns, four in each wing. It had a maximum speed of 335 mph at 18,000 ft and an operating ceiling of 35,000 ft.

The Spitfire was designed by Reginald Mitchell and first flew in March 1936. It entered service with the RAF during 1938, and there were many similarities with the Hurricane; the engine and armament, for example, were the same. However, the aerodynamic design and lower wing loading of the Spitfire gave it better performance and a greater turning advantage. More importantly, it meant that the Spitfire was more manoeuvrable than the Bf109 at all heights. It had a top speed of over 350 mph at 19,000 ft and an operating ceiling of 34,000 ft. It could reach an operating height of 20,000 ft in about nine minutes. Production figures for the Spitfire during 1940 were not as high as for the Hurricane (about eighty per month compared to a peak of nearly 250 per month for the Hurricane), which meant that there were fewer Spitfire squadrons during the Battle of Britain – although the Spitfire accounted for more than half of Fighter Command’s successes.

The Bristol Blenheim IF was used as a night fighter, even though it had been designed as a high-speed light bomber. It first flew in 1936 and was powered by two Bristol Mercury engines, which gave it a speed of up to 275 mph at 15,000 ft and an operational ceiling of 25,000 ft. It was fitted with a semi-retractable, hydraulically operated dorsal turret with a single Vickers K gun. Because it had suffered losses during daylight operations over France, it was only used at night during the Battle of Britain, as it was considered to be no match for the Bf109. In the night fighter role it was converted from the standard Mk I aircraft to the Mk IF by the addition of four 0.303 in Browning machine guns mounted in a ventral pack under the centre fuselage. The development of airborne radar led to its installation in the Blenheim IF and there was the occasional success.

The fourth fighter used during the battle was the Boulton Paul Defiant I, which first flew in 1937. Initially its performance was considered to be very good in terms of speed and flying characteristics. It was powered by a Merlin engine, as fitted to the Spitfire and Hurricane, and could achieve a speed of just over 300 mph at 17,000 ft, with an operating ceiling of 30,000 ft. It entered operational service with the RAF early in 1940 and it was involved in the air war over France. Two squadrons were equipped with the Defiant during the Battle of Britain but its performance proved to be one of the biggest disappointments to Fighter Command; it suffered disastrous losses when up against the Bf109. Its concept of operating as a two crew aircraft (pilot and air gunner) proved problematic, it had no forward firing armament but instead had a hydraulically operated rear-mounted turret with four 0.303 inch Browning machine guns. It was up to the pilot to position the aircraft and the gunner to bring its armament to bear. Following disastrous losses it was soon withdrawn from daylight operations, but it did later operate at night.

Britain's Defence System

The technical development of radar had provided Britain with the capability of early warning of attack, which compensated for the RAF’s numerical disadvantage. This meant that the RAF could avoid having fighters continuously in the air over southern England to protect its Channel ports, airfields, industrial installations, and the south’s heavily populated towns and cities. This would not only have proved costly in vital resources such as fuel but increasing fatigue would gradually have drained the pilots over a period of time. However, pilots had to be kept at readiness, which made it essential for No 11 Group to keep all its airfields open.

By July 1940 a chain of detection stations had been established between the north-east and south-west of Britain, known as Chain Home. The transmitter aerials were on steel towers about 350 ft high and the receivers were on wooden towers about 240 ft high. Detection was possible out to a range of about 100 miles, depending on the height of the aircraft. However, detection of low flying aircraft was not possible and so Chain Home Low was developed with a range of up to 50 miles, although the height of aircraft could not be accurately determined. The aerials detected formations of aircraft as they formed up across the Channel over northern France. The operator was presented with a V-shaped ‘blip’ on a cathode ray tube display in a building known as the Receiver Block. From there information was passed to the Filter Room at Bentley Priory and then to No 11 Group at Uxbridge. It was from there that the duty controller would alert the appropriate sector airfield, which then scrambled and directed the various squadrons. The system and process was designed so that the time taken from receipt of a radar ‘blip’ to alerting the squadron best placed to deal with the threat was less than six minutes. It is also worth mentioning at this point that by the beginning of the Battle of Britain all of Fighter Command’s fighters had been fitted with Identification Friend-or-Foe (IFF) to help avoid confusion between ‘friendlies’ and ‘hostiles’.

There were sixteen radar sites within No 11 Group’s area of responsibility, eight of which were high level sites (Chain Home or CH) and eight low-level (Chain Home Low or CHL). From Suffolk, working clockwise they were: Dunwich (CHL), High Street (CH), Bawdsey (CH), Bromley (CH), Walton (CHL), Canewdon (CH), Dunkirk (CH), Foreness (CHL), Dover (CHL), Rye (CH), Fairlight (CHL), Pevensey (CH), Beachy Head (CHL), Truleigh (CHL), Poling (CHL) and Ventnor on the Isle of Wight (CH).

In addition to the radar sites, the Observer Corps also watched the skies over southern England. They used binoculars to spot the small specks in the sky, which grew increasingly larger as formations of enemy aircraft approached. They communicated by telephone with the Observer Corps centres and provided warning of attack, giving numbers, heights and types of enemy aircraft. Used with the information provided by the early-warning radar sites, and any information from patrolling fighters, this was a vital input to help develop the air picture. The accuracy of the Observer Corps input to the overall air picture depended mostly on visual information and was obviously restricted during cloudy conditions or at night. But all this information had to be put together to make sure that the fighters were in the right place at the right time.

The heart of Britain’s defence system was Fighter Command’s filter room at Bentley Priory. Information from the various sources was presented on a large plotting table showing an outline map with an arrangement of coloured discs to represent enemy formations. Red, yellow or blue were used to represent periods of time, each of five minutes, so that controllers could tell the history of the tracks, which would never be more than fifteen minutes old. Woman’s Auxiliary Air Force personnel (WAAFs) moved the counters around the plotting table using magnetic rakes. Sitting above the plotting table and watching over events was the duty controller and other officers with telephones connecting the filter room with Group headquarters.

Information would pass from Bentley Priory to Uxbridge, which in turn passed the relevant information to the appropriate sector airfields (each with its own operations room), which then alerted the squadrons. Known affectionately as ‘the hole’, the air-conditioned operations room at Uxbridge had been constructed two storeys underground. It was relatively compact and measured 60 ft across. The duty controller sat on a raised dais next to a bank of telephones, which linked the sector airfields. On the opposite wall was a status panel, which had light bulbs to show the status of every squadron within the group. Again, a colour system was used to show the duty controller the history of the information, which again was never more than fifteen minutes old. The WAAF plotters listened through headphones and marked the state of the air battle on a large map below, using long croupier rods to move the various coloured discs around the map. A four-watch system was used for those working in the bunker, with individuals on an eight-hour shift during the 24-hour period, with one shift off at any one time.

Throughout the period of the battle, squadrons were rotated depending on their strength at any one time and dispersed assets when the airfields became priority targets. Those squadrons in the forefront of the action often moved several times. Nevertheless, the RAF maintained the advantage of operating close to home. Its fighters could land back at base, or elsewhere if necessary, to refuel and rearm, and then be back in the air in a relatively short space of time. Readiness states of the squadrons varied; the highest was ‘stand by’, with the pilot in the cockpit facing into the wind ready to start his engine immediately and take off. The obvious disadvantage for the pilot was that he was often sitting in a very warm cockpit and was not able to stretch out or relax, which meant that this state of readiness could only be maintained for short periods at a time. The next state was ‘at readiness’, with the pilots at the squadron dispersal, ready to be airborne within five minutes. The more relaxed state was ‘available thirty minutes’ with the pilots at the Mess, ready to be airborne within thirty minutes.

Britain’s defence system also included searchlights and anti-aircraft guns to defend the cities, plus many lighter guns to protect the airfields. Anti-aircraft Command was under the command of Lieutenant General Sir Frederick Pile, and had its headquarters at Stanmore. Responsibility for the protection of London belonged to the 1st Anti-Aircraft Division, with more than 120 heavy guns. The rest of the south-east was the responsibility of the 6th Anti-Aircraft Division, with nearly 200 heavy guns, mainly old 3 in guns plus the newer 3.7 in and 4.5 in ones. In addition there were a few hundred more light guns (mainly two-pounders and Bofors 40 mm) and several hundred light machine guns protecting the airfields and other key targets.

No 30 (Balloon Barrage) Group was also responsible for the protection of London and the south-east of England with more than 500 balloons, which were able to reach heights of up to 5,000 ft. They were not there in the hope that an attacking aircraft would fly into one, or its cables, but more to keep them at height so that bombing accuracy was more difficult. During the period of the Battle of Britain, bombing techniques from medium level were basic. Whilst the Luftwaffe crews could attempt to put bombs within an airfield boundary, there was no guarantee of hitting any specific targets such as runways, hangars or technical buildings. Even leaving craters across the airfield would not necessarily prevent fighter operations. However, attacks from low level caused most damage, and it was necessary for No 11 Group’s airfields to have good defences.

Whilst the number and type of defences varied from airfield to airfield, those at Kenley provide a good example. Its main airfield defences consisted of two 3 in anti-aircraft guns manned by the 148th Light Anti-Aircraft Battery, four smaller 40 mm Bofors guns manned by the 31st Light Anti-Aircraft Battery and several Lewis machine guns. There was also a parachute and cable installation, known as PAC, which fired salvos of rockets at any raiders at low level. The rockets were designed to reach a height of about 500–700 ft. The parachutes would slow down the rate of descent of the steel cables and the hope was that low-flying aircraft would fly into them. PAC did have some success and it is credited with bringing down a Do17 in a low-level attack against Kenley during the early afternoon of 18 August. In addition to the one brought down, a second was hit and crashed near Biggin Hill.

In addition to the airfield defences were the local defences. All along the coastline of south-east England there were the Home Defences, although only one in three individuals had a rifle. The Army was not in a much better position, with so much equipment having been lost during evacuation from Dunkirk. There was just one machine gun for every mile along the coast but every possible way of obstructing an enemy invasion and subsequent advance was used.

Air Vice-Marshall Keith Park.

'When the Battle of Britain opened, No 11 Group had approximately 350 aircraft and twenty-two squadrons: thirteen equipped with Hurricanes, five with Spitfires, three with Blenheims and one with Defiants.'

Battle of Britain newsreels.

Illustrations by Jon Wilkinson.

Hawker Hurricane Mk I (top) and the Supermarine Spitfire Mk I.

Illustration by David Lee Hemingway.

Boulton Paul Defiant I.

Radar masts on the south coast of England.

Men of the Observer Corps plotting aircraft in 1940.

Plotting table at Bentley Priory.

AA guns were positioned in Hyde Park for the defence of London.

Barrage balloons about to be raised over a British airfield.

'Whilst the Luftwaffe crews could attempt to put bombs within an airfield boundary, there was no guarantee of hitting any specific targets such as runways, hangars or technical buildings.'

Ready to repel the invader. A cliff-top Lewis Gun position somewhere on the south coast.

'All along the coastline of south-east England there were the Home Defences, although only one in three individuals had a rifle.'

Photograph colouring by Jon Wilkinson.

Battle of Britain- Airfields of 11 Group

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The Battle of Britain - Britain's Defences, 1940

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