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Dowding system

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Subject: Battle of Britain, Pip-squeak, Comprehensive Display System
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Dowding system

This illustration shows the Dowding reporting chain for a highlighted Sector. ROC reports flow back through the Sector controls to FCHQ; it does not show the radars. Information flows back from FCHQ to Group, between groups, and down to Sectors, and then to the defences.

The Dowding system was the world's first wide-area ground-controlled interception network,[1][1] controlling the airspace across the UK from northern Scotland to the southern coast of England. It used a complex private telephone network to rapidly collect information from Chain Home (CH) radar stations and the Royal Observer Corps (ROC) to direct defensive interceptor aircraft and anti-aircraft artillery. The system was built by the Royal Air Force just before the start of World War II, and proved decisive in the Battle of Britain.

The Dowding system was developed after tests demonstrated problems relaying information to the fighters before it was out of date. Air Chief Marshal Hugh Dowding, commander of RAF Fighter Command, solved the problem through the use of hierarchical reporting chains. Information was sent to Fighter Command Headquarters (FCHQ) central filter room at Bentley Priory and used to prepare a map of the battle. Details of the map were then relayed to the Group and Sector headquarters, where operators re-created the map at a scale covering their area of operations. Looking at the maps, commanders could make decisions on how to employ their forces quickly and without clutter. Instructions were relayed to the pilots only from the squadron's sector control rooms, normally co-located at the fighter's operating bases.

The Dowding system is considered key to the success of the RAF against the German air force (Luftwaffe) during the Battle of Britain. The combination of early detection and rapid dissemination of that information acted as a force multiplier, allowing the fighter force to be used at extremely high rates of effectiveness. In the pre-war period, interception rates of 30% to 50% were considered excellent; that meant that over half the sorties sent out would return without having encountered the enemy. During the Battle, average rates were well over 80%, and several raids were met with 100% success rates.[2] Lacking their own direction system, Luftwaffe fighters had little information on the location of their RAF counterparts, and often returned to base having never seen them. When they did, the RAF fighters were almost always in an advantageous position.

Although many histories of the Battle of Britain comment on the role of radar, it was only in conjunction with the Dowding system that radar could be truly effective. This was not lost on Winston Churchill, who noted that:

"All the ascendancy of the Hurricanes and Spitfires would have been fruitless but for this system which had been devised and built before the war. It had been shaped and refined in constant action, and all was now fused together into a most elaborate instrument of war, the like of which existed nowhere in the world"[3]


Previous work

Through the 1920s and 30s, the defense against air attack had been run by a War Office department known as Air Defence of Great Britain (ADGB). In 1936 its duties were handed to the Air Ministry, and divided into Fighter Command and Bomber Command. Dowding was promoted to Air Officer Commanding-in-Chief of the Fighter Command on its creation on 6 July 1936.[4]

Part of the earlier ADGB that Dowding inherited was the the London Air Defence Area, a defensive system first built by E.B. Ashmore in World War I to protect London.[5] Ashmore had divided defensive weapons into three rings around the city; the outermost ring held searchlights and anti-aircraft artillery, the middle ring was the operating ground for fighters, and the innermost, in the city itself, contained additional guns.[6] In order to communicate the location of the targets to the weapons, Ashmore set up a large plotting table in the Horse Guards in London. Information from spotters was relayed to this central control room within thirty seconds, where wooden blocks were placed on a large map in order to indicate the location and other information. Observers around the map could relay this information to one of 25 regional control rooms, who re-created the portions of the map of interest to them, and relayed that information to the various weapons in their region.[6]

Throughout this period various commenters noted the serious problem that the system lacked a form of early detection, which was deemed essential as the performance of aircraft improved.[7] Numerous experiments with acoustic mirrors and similar devices were carried out almost continually, but these always proved unsatisfactory, with detection rates often as low as 5 miles (8.0 km). In spite of this, lacking any other solution, in December 1934 the Air Ministry made plans to deploy sound detection devices around London as part of the Thames Estuary plan.[7]


Prior to being promoted to lead Fighter Command, Dowding had been the Air Member for Supply and Research. In early 1935 he had been introduced to the idea of what was then known as RDF by members of the Tizard Committee. Robert Watson-Watts researchers continued to improve its performance through the early part of the year, and by late in the year plans were already being drawn up to create a string of RDF stations under the code name Chain Home. By the end of the year the detection range had been extended beyond 100 miles (160 km), giving Fighter Command ample warning time of an impending raid. In spite of rapid progress, RDF continued to demonstrate several problems. In one infamous example, Dowding was watching the displays of the test system at the development center at Bawdsey Manor for any sign of the attackers when he clearly heard them approaching overhead.[8]

As early as 27 July 1935, Henry Tizard suggested running experiments to test the practicality of the interception system, based on an estimated fifteen minute warning time that radar would provide. This led to a seven-month long series of experiments at Biggin Hill, under the direction of Wing Commander Eustace Grenfell aided by navigation expert Squadron Leader Robert Linton Ragg.[9] In these experiments, Gloster Gauntlet fighters were tasked with intercepting virtual aircraft, civilian airliners, and finally Bristol Blenheim light bombers.[4]

At first the interceptions were calculated using trigonometry and mechanical calculators, but eventually Grenfell had enough of the "confounded machines", and proceeded to arrange a perfect interception by eye.[10][2] Tizard introduced the equal angles method of rapidly estimating an interception point, by imagining the fighters and bombers at the opposite corners on the base of a triangle. The bombers were flying at a particular angle to the base, and the commander simply had to send the fighters on the opposite angle, so the two would meet at the apex of the triangle. With this "Tizzy Angle", interception rates shot up, and by the end of 1936 they were consistently above 90% as long as the altitude was known and did not change. If the bombers changed their altitude, or the fighters arrived below them, repositioning for the attack reduced the success rate to about 60%.[11][3]


Dowding's strong support for radar was matched by his understanding that radar alone was not a complete solution.

In spite of rapid progress, RDF continued to demonstrate several problems. In one infamous example, Dowding was watching the displays of the test system at the development center at Bawdsey Manor for any sign of the attackers when he clearly heard them approaching overhead.[8] These problems were ironed out over the next year, and in April 1937 a series of full-up tests using the prototype CH radar at Bawdsey demonstrated great promise, allowing the controllers to estimate the altitude of the aircraft within 2,000 feet (610 m), which greatly reduced the problems seen earlier.[11]

CH was also a fairly short range system, so in order to increase warning time the CH systems were sited on the shoreline, looking out to sea. This meant that it provided no location information for friendly fighters on the way to the attack, nor location information for any aircraft over land. To address this later problem, the newly formed Royal Observer Corps (ROC) was tasked with maintaining information on the aircraft once they were over the British Isles. This led to another serious problem; using different systems, the reports from CH and the ROC were sometimes contradictory or wrong. Also, the volume of information supplied by the now-national network was overwhelming.[12]

CH also, initially, had no way of identifying friendly from enemy aircraft. This problem had been considered throughout the development of CH and several solutions had been introduced that produced unique shapes for the radar returns of friendly aircraft. However, as the radars looked out to sea, these systems were of no use when the fighters were over land, or even near the coast. The ROC could not discriminate between friendly and enemy fighters either as they were too small to see clearly when flying at high altitudes.

Dowding immediately set about attacking these problems. To address the sheer volume of reports, and the potential for overlap, he instituted the policy of sending all location reports to the new direction centre at Fighter Command headquarters. Here the data was collated and filtered to produce accurate plots and tracks. The data was then sent, on demand, to the group headquarters, and then to the sectors (see below). To fix the problem of locating friendly aircraft, Dowding pressed for a supply of high-frequency direction finding ("huff-duff") sets, which could locate the fighters using their existing radio sets. This led to the introduction of the "pip-squeak" system that was widely available from early 1940, along with the first identification friend or foe (IFF) transponders which were widespread by October 1940.[13]

By early 1939 the basic reporting system was in place, and from 8 to 11 August 1939, RAF Bomber Command was asked to launch a series of mock attacks using aircraft returning from exercises over France. Reports from No. 11 Group RAF were extremely positive, stating that "RDF information and plotting throughout the Exercise was consistently first-rate, and enabled interceptions to be effected on the Coast", to which Dowding added "daylight raids were normally tracked and intercepted with ease and regularity".[13]



The first improvement Dowding suggested was implemented by adding a filter room at FCHQ where all CH reports were sent.[14] Here, all incoming reports were plotted on a large map using small markers representing the number and type of aircraft and other information. The reports were sent to them in the form of Ordnance Survey National Grid locations,[5] which required some work on the part of the observers to translate from their range and azimuth measurements. The plotters placing the markers did not filter anything, every report was placed on the map. Since different plotters were communicating with different sources, CH or ROC for instance, the rapidity of the reporting caused the plot markers to pile up on the map, which became quite cluttered during larger missions. Since each of these reporting systems would have slightly different measurements, the plots were not at a single spot, but spread out.[12]

Observers watching the progression of plots being placed would try to determine which of these represented the same group of aircraft. When they were confident that a certain group of markers was a single formation, a wooden block was placed on the map in the middle of the plots, with markers holding the information for type of aircraft, number of aircraft, and altitude. Each one was given a number, the track number. The block would be periodically moved or updated as further plot markers were placed on the board, and as it moved the plotters would leave behind small arrow-shaped pointers to illustrate where it had been.[12]

Around and above the map were a number of telephone operators, or tellers, who controlled the communications, connecting incoming reports to the plotter on the floor nearest that location on the map, or alternately connecting incoming requests for information to another teller who could read the map. To do this, the tellers would examine the track markers, who's larger print allowed them to see the information, although this sometimes required opera glasses.

Sometimes information would have to be plotted that came from an external source that was not normally part of the reporting chain. For instance, a fighter calling an SOS would report this through his radio on an emergency frequency which would be picked up by the closest listening post. This information would also flow into the filter room, but they were not connected to the plotters on the floor. In these cases, operators above the map could mark locations of interest using theatrical spotlights, and a series of filters allowed them to change the message being projected on the map, typically one of a number of single letters.

Reporting hierarchy

11 Group's Operations Room in the Battle of Britain Bunker. On the plotting table are numerous plots. The sector clock on the wall behind the map has coloured regions matching the colours on the plots. Above the clock is the main tote board showing the status of the various airfields and their squadrons.
A wooden marker on a map, surrounded by several others.  Below and to the right is a cue with a wooden slab on the end, used to move the markers.
Close-up of a marker for friendly fighters. It indicates that 20 enemy (red) aircraft at 25,000 ft (7,600 m) are being intercepted by 92 and 72 Squadrons of Biggin Hill.

The second improvement introduced by Dowding was aimed at reducing the amount of information being sent to the pilots, and speeding its delivery. For this task, Dowding introduced a hierarchy of control and information flow which ensured that only the information the pilots needed was forwarded to them. At the topmost level was FCHQ filter room, located at Bentley Priory. FCHQ maintained an overall view of the entire battlespace. This information was then forwarded one step down a hierarchy, to the Groups.[5]

During the Battle of Britain the defensive fighters were split among four active Groups, 10 through 13. 11 Group, which handled most of the fighting, was located in the Battle of Britain Bunker (RAF Hillingdon) at Uxbridge, not far from FCHQ. 12 Group, covering the Midlands, was located at Hucknall (and later Watnall), 13 Group in a quarry in Blakelaw outside Newcastle, and the late-formed 10 Group in the aptly named Box outside Bath.[5]

At the Group HQs another plotting board, covering only the area of interest to that Group, re-created the plots from FCHQ via position reports sent to them over the telephone. This allowed the Groups to re-create the map, but on a scale and location more suitable to their area of operations.[15] Since the information was being pre-filtered, these maps did not have to be changed as often, and a somewhat simpler marker solution was adopted. Small wooden blocks with tags were placed on the map to represent the location of various formations, indicated by the ID number created in the filter room. The tags indicated the ID number, friend or foe status if known ("H" meant "hostile, F for "friendly"), the estimated number of aircraft, and their altitude. The color of the altitude tags indicated when the report was updated, the colours matching a large sector clock on the wall. This allowed observers to quickly determine whether or not a plot was up to date.[16] If a target was assigned squadrons for interception, these were indicated with cocktail stick-like tags with the squadron number on them.[17]

Each Group was split into several Sectors, which handled operations for one or more airfields. This formed the lowest level of the hierarchy, based at the Sector Controls, normally co-located at one of the sector's airfields. For instance, 11 Group was split into sectors A through F running anticlockwise from the south-west to north-east, along with Sector Z to the northwest. A typical sector, Sector C which saw considerable action, was controlled out of Biggin Hill, but also contained another major airbase at West Malling (Maidstone).[5] Telephone links from Sector to Group allowed the Group's version of the map to be re-created at the Sector, again filtering out information that was not of interest in that area.[18]

It was the Sector Controls that were responsible for communication with the pilots, as well as balloon barrage and anti-aircraft artillery batteries, providing early warning of the approach of the enemy or warning them not to fire on friendlies.[5] In order to combat the problem that the fighter pilots tended to ignore orders from paper pushers, Sector Commanders were normally former pilots themselves, either retired or on medical leave. Dowding, Patrick Blackett and Henry Tizard personally drove home the fact that the pilots could not simply hunt for their targets, and had to follow the instructions of the operations centers.[12]

By creating this system, information flow was primarily in one direction, and continued to be split out on the way down. For instance, the filter room might be receiving 15 reports per minute from various CH sites, but these would be about formations that might cover the entire coast of Great Britain. Portions of these reports, say those over Kent, would be sent to 11 Group, while others, the attack on RAF Driffield for instance, would only be relayed to 13 Group. In turn, 11 Group's operations room would relay only those tracks of interest down to the sectors, filtering out tracks that were out of their range, or being handled by other sectors. Finally, the sector operators only had to relay information to the pilots that actually had an effect on their flight – data about other formations was not relayed, freeing the radio time.

Information sources

The tall towers of the Chain Home system allowed them to detect targets as far as 100 miles away, over France.
A ROC Post Instrument plotter, with Mickelthwait height adjuster attachment. ROC reports began to flow in as the enemy approached the shoreline.

Chain Home offered an enormous improvement in early detection times compared to older systems of visual or acoustic location. It was not uncommon for CH stations on the southeast coast of Kent to detect enemy raids as they were still forming up over their airfields in France. Additionally, this information was available day or night, in any weather. However, in order to provide maximum warning time, the CH stations had to be placed as close to the shore as possible. As they could only locate objects in front of them, this meant that CH provided no service over land. This required two additional locating services.[5]

The task of tracking enemy aircraft over land fell to the Royal Observer Corps. Because of the large number of ROC stations and the relatively small areas they covered, information duplication and overload was a concern. For this reason, information from the ROC was sent to a parallel system of Observer Centres, who acted as both filter and communications stations. This pre-filtered information was then sent into the Dowding reporting chain.[5][4]

Likewise, a separate reporting chain was tasked with tracking friendly aircraft through the use of radio direction finding (RDF) on their radio transmissions, using a system known as "Huff-Duff" (receivers) and "pip-squeak" (transmitter).[16] Developing a fix using RDF requires two or more observation locations spread apart by some distance and then using triangulation on their reports. In this case three stations were typically used, located about 30 miles (48 km) apart. This information was reported to a selected Sector Control, who used this to plot their locations and pass on that information to the main operations plot. Controllers could then give directions the squadrons. Locations of the fighters were sent up the chain only as required.[19]

Finally, information on the status of the fighter squadrons was known to the Sectors but needed by the Groups in order to choose which squadrons to commit. For this task, operations rooms also contained a series of blackboards and electrical lamp systems indicating the force strengths of the fighter squadrons and their current status. Known as the "tote board", this allowed commanders to tell at a glance which units were available to receive commands. The statuses were Released (not available); Available (able to be airborne in 20 minutes); Readiness (airborne in 5 minutes); Standby (pilots in cockpit, airborne in 2 minutes); Airborne and moving into position; Enemy sighted; Ordered to land; Landed and refueling/rearming. Next to the tote board was a weather board. It was the responsibility of the Women's Auxiliary Air Force (WAAF) plotters[5] to continually update the tote and weather boards, and relay that information up the chain.[20][21][6]

Command and control

The Group Control room for No. 10 Group in RAF Box in Wiltshire. This was one of the best developed control rooms.
The Sector Control room at Duxford controlled the area from London to The Wash. Radio and telephone operators sat on the upper level, with plot operators in the white chairs.

The most visible part of the Dowding System were the "operations rooms". The most advanced of these were located at FCHQ and Group HQ's. These rooms typically consisted of three layers: a large plotting table on the lowest level, communications operators located at desks around and above the plot but in the same room, and finally a second story located above the plot and sometimes isolated behind glass.[16]

Actual command control over the battle was devolved to the Group level.[14] Observing the map from above, Group Commanders could track the movements of enemy aircraft through their airspace. When the time was right, they examined the tote board, selected an available squadron, and called their Sector to have them scramble. The orders could be as simple as "Squadron nine-two, intercept hostile two-one".[18] The Sector would then phone the office for that squadron (often nothing more than a small shack) and ask for the planes to be scrambled.

After forming up the Sector Controller would ask the squadron to set up their pip-squeak system so they could be tracked accurately. Once their location was measured and transferred to the sector plotting table, the controller would begin to relay instructions to the squadron leader. The vectoring was accomplished using the methods developed in the Biggin Hill exercises in 1935, with the Sector Commander comparing the location of the friendly aircraft with the hostile plots being transferred down from Group, and arranging an interception.[10] As the fighters were faster and often flew to the interception point first, they were instructed to orbit the location, which allowed them time to climb and seek an advantageous position.

Squadrons, bases and enemy formations were all assigned code words aimed at easing communications speed and accuracy. Updates from sector control at Biggin Hill to 72 Sqn would take the general form "Tennis leader this is Tophat control, your customers are now over Maidstone, vector zero-nine-zero, angels two-zero". This indicated that Biggin Hill's controller (Tophat) was asking No. 72 (Tennis) to fly due east (vector zero-nine-zero) at 20,000 feet (angels two-zero) to intercept their target. The sector was also responsible for local gun and balloon defences, as well as ensuring the fighters could be safely returned to an airfield after their sortie.

Physical construction

The entrance to Group 11's operations room, which was completely underground.

FCHQ and Group Control centres, in keeping with their importance in the battle, were located in bomb-proof bunkers away from airfields. Most of these were built just before the war. Communications were ensured by hundreds of miles of dedicated phone lines laid by the GPO and buried deep underground to prevent them from being cut by bombs.

Sector Control centres tended to be relatively small, and were mostly housed in brick, single-storey, tile-roofed structures above ground, where they were vulnerable to attack. By 1940, most were semi-protected by an earth bank or "blast wall" surrounding them which reached as high as the eaves. Fortunately, Luftwaffe Intelligence was unaware of the importance of these rooms and most were left alone.

The control rooms at Biggin Hill were destroyed by a raid on 31 August, but this was due to a chance bomb hit. As a further precaution, emergency control rooms were set up in different locations away from the airfields, with small loss in efficiency; Kenley, for example, could use an alternative room housed in a butcher's shop in nearby Caterham.[21]

The vulnerability of the earlier rooms was appreciated, and new airfields built during the expansion programme of the 1930s used bombproof Mk. II, L-shaped structures.

Effects on the battle

German Freya early warning radar. Early detection alone was not enough, however, inasmuch as appropriate exigent information needed to be relayed to the pilots.

The effect of this system was profound, and remains a widely used example of the concept of force multiplication.[22] Before the introduction of radar the task of interception appeared to be increasingly difficult, if not impossible. As bomber speeds and altitudes grew, even the increased performance of the fighters meant that the available interception time was dropping – certain aspects like getting the pilot into the aircraft and taking off introduced fixed overheads that did not improve along with the aircraft. With the only detection means being the observers and acoustic location with ranges on the order of 20 mi (32 km) under the very best conditions, the bombers would be over their targets before the spotters could call in the raid and the fighters could climb to their altitude.[2]

Given this lopsided balance of power, fighter operations prior to the introduction of radar were generally in the form of "sweeps", with the fighters being sent up to fly along a pre-arranged path or area in the hopes of encountering the enemy. During WWI interception missions, the vast majority of patrols returned home without ever having seen the enemy. The same was true for all forces during the Battle of France, where 30% interception rates were considered typical, and 50% excellent.[2]

In the case of an attack by a high-speed force, the attackers could pick the time and place of the attack, and expect to encounter only the aircraft already in the air along that route. In order to ensure there were a reasonable number of fighters along any approach route, huge numbers of aircraft would need to be in the air at all times covering all the routes. Even more aircraft would be needed to handle issues like refuelling and repair. Likewise, a huge number of pilots would be needed to crew the aircraft, as each pilot could only be expected to fly so long per day. Such a system was essentially impossible, and was one of the reasons it was widely believed "the bomber will always get through".[23]

The unified view of the battlespace provided by the Dowding system turned the tables in favour of the defence. By rapidly sending accurate, timely information to the fighters, their ability to find and attack the enemy was dramatically increased, and the time required to do so decreased. The fighters took off, flew directly to their targets, engaged and returned directly to their bases. In early operations interception rates of 75% were routine, and this number continued to improve as the operators became more familiar with their tasks. By the end of the Battle of Britain, rates of interception over 90% were becoming common, and several raids were met with 100% interception rates.[2] In numerical terms, it was as if Fighter Command had over twice as many fighters, giving them effective parity with the Luftwaffe.

While CH was being installed in the UK, the Germans were working on their own radar systems and had deployed an excellent early-warning system known as "Freya". But the complexity of relaying the information from the radars to the fighters had not been addressed, and was apparently never seriously considered at the time. During the Battle of the Heligoland Bight in 1939, over 100 German aircraft were scrambled to meet a small force of RAF bombers, but less than half of these found them. This was in spite of a Luftwaffe Freya radar detecting the raid while still one hour out; this unit was unable to communicate with the fighters. The only radar reports to reach them came from a naval Freya near the target, too late to improve matters.[24]

Likewise, the Opana Radar Site detected the attack on Pearl Harbor long before it reached the island. They did have a telephone available, and called the communications office that was in charge of disseminating such information. The office had been informed that a flight of B-17 Flying Fortress bombers would be arriving that day, but lacked any sort of information on their location, at that time far to the east. The communications officer, Lt. Kermit Tyler, concluded the radar site had spotted the bombers, and failed to pass on the warning. The Japanese attack went unopposed.[25]

It was only through the combination of all of the elements of the Dowding system that an effective defensive network was created. Peter Townsend later noted that:

The Germans knew about British radar but never dreamed that what the radar 'saw' was being passed on to the fighter pilot in the air through such a highly elaborate communications system.[14]

During the war, the Luftwaffe consistently underestimated the value of the system. A 16 July 1940 Luftwaffe intelligence report failed to even mention it, in spite of being aware of it through signals intercepts, and having complete details of its WWI predecessor. A later report on 7 August did make mention of the system, but only to suggest that it would tie fighters to their sectors, reducing their flexibility and ability to deal with large raids.[26]

While discussing the events with British historians immediately after the war, Erhard Milch and Adolf Galland both expressed their belief that one or two CH stations might have been destroyed during early raids, but they proved difficult targets. This was true; several stations had been knocked out of service for a time, while others managed to maintain operations in spite of attacks. But the historians interviewing them noted "neither seemed to realize how important were the RDF stations to Fighter Command technique of interception or how embarrassing sustained attacks upon them would have been."[26]

This realization must have sunk in over time; after the war Galland noted:

From the first the British had an extraordinary advantage, never to be balanced out at any time during the whole war, which was their radar and fighter control network and organization. It was for us a very bitter surprise. We had nothing like it. We could do no other than knock frontally against the outstandingly well-organized and resolute direct defence of the British Isles.[27]


Although the Dowding system proved itself in combat, the system and the overall command of the battle presented several problems.

A major issue was the volume of information that flowed through the system, especially into the FCHQ filter room. On 11 January 1940 an operations research (OR) report on the Dowding system pointed out that the filter room had originally intended to correlate radar reports, but had developed into something much more complicated. As a result too much control was placed in the filter room, which was producing results with "appallingly low standards". Given its success in practice, it is not clear whether the report was inaccurate or if the problems had been addressed by the time of the Battle.[28]

Additionally, it was well recognized that the filter room could be overwhelmed in battle due to the volume of reports. Numerous complaints about the single point of failure it represented were brought up from many commenters, from the OR reports to many within the RAF and Air Ministry establishments. Most demanded that the filter room be devolved from Bentry Priory to the local Group commands, lowering the reporting volume at any one location, and providing duplication. Dowding refused any such change, leading to increasing friction with other commanders. Information overload actually occurred on several occasions and the filter room had to ask certain CH stations to stop reporting, but in practice this problem had little effect on their capabilities. Such events were later handled by having stations report only basic information for multiple formations as a single plot.[28]

Another problem was due to the limitations of the TR.9D HF radio set equipping fighters at the time of the Battle of Britain. This system had two channels, and the operating frequencies of the two could only be selected before the mission. One of the channels was used for voice communications with their Sector Control, while the other was used for the "pip-squeak" system. With only a single usable voice channel, set to a squadron-specific frequency, the TR.9D limited the ability for friendly aircraft to coordinate. The set also had limited power, offering effective range of about 40 miles (64 kilometres) air-to-ground and 5 miles (8.0 kilometres) air-to-air (a function of the antennas used in air and on the ground), which presented numerous problems with reception quality. Making matters worse, the TR.9 had originally operated in a band that was relatively unused, but by the time of the war it had become widely used and interference was a constant problem.[29]

Chain Home, while providing invaluable information, could only do so for aircraft in "front" of the antennas, typically over water off the shores of the UK. This meant that the system relied on the ROC once the raid was over land. The ROC, using visual means, had limited to no ability to provide information at night, in bad weather, or even through local overcast. This was not a major concern during the Battle of Britain, as the weather was unusually good,[30][7] the so-called "fighter's summer", and the raids being attacked took place only when the weather allowed the bombers to see their targets.[31] The system failed to work against high-altitude raids that took place late in the Battle, and was entirely useless during poor weather or at night.

Finally, the effectiveness of the response as a whole was affected by inter-group rivalries within the RAF command structure. This was especially true for the critical areas covered by 11 and 12 Groups, whose commanding officers were involved in a constant fight. Trafford Leigh-Mallory, commander of 12 Group, had originally been slated to take over the key 11 Group command before the war, but was instead replaced by Keith Park. Leigh-Mallory felt further slighted by Dowding, because his 12 Group was tasked with defending 11 Group's airfields while 11 Group attacked the enemy.[32]

Dowding had failed to set a command structure starting at FCHQ, which meant that every Group commander was able to control their own battle. Group commanders could request, but not demand, support by other groups. During the battle, Leigh-Mallory repeatedly failed to send his fighters to support 11 Group's airfields, preferring instead to build his "Big Wing" formations and directly attack the enemy. These formations took considerable time to build, and were often still forming as the enemy flew away. In the end they contributed little to the early stages of the battle.[32] Dowding's inaction on this front was one of the strikes against him that ultimately led to his removal from Fighter Command.

After the Battle

GCI radars allowed a single station to provide detection, identification (IFF) and fighter direction, eliminating the need for the complex reporting chains of the Dowding system.

Throughout the use of the system, Dowding constantly had to fight off suggestions that the filter room be moved to the Group level. This would reduce demand on FCHQ's filter room, as well as provide redundancy. This issue came up several times, the last time on 27 September 1940, when the Air Council's request was once again dismissed by Dowding. This led to his summons to the Air Staff on 1 October, when he was forced to devolve command, although he delayed this until all fighters were equipped with new IFF systems.[28]

Only a few weeks later, Dowding was removed from command, perhaps due in part to his failure to come up with solutions to The Blitz. Within months, the Groups had received their own filter rooms. The introduction of ground-controlled interception radars (GCI) in the winter of 1940/41 further devolved command by allowing sector controls to directly detect and control the aircraft in their area.[28] Working in concert with IFF, now widely available, the GCI display eliminated the need for separate detection and plotting, as well as the communications links and manpower needed to operate the reporting system.

In the post-war era the entire fighter control system was quickly demobilized. However, the explosion of the Soviet atomic bomb in 1949, and the presence of Tupolev Tu-4 "Bull" aircraft that could deliver it to the UK, led to the rapid construction of the ROTOR system. ROTOR re-used many of the existing GCI and CH systems, but built dramatically upgraded control rooms in hardened underground bunkers. ROTOR was in turn replaced by the Type 80 radar Master Control rooms, and then the Linesman/Mediator system in the 1960s.


  1. ^ The term Dowding system is a modern one, there was no official name for the network at the time.
  2. ^ In Fighter Len Deighton suggests that Grenfell developed the equal angles method. All sources included here give precedence to Tizard, but do not specifically state that he introduced it to Grenfell.
  3. ^ Zimmerman notes that the reason for this drop in success rate was due to a lack of DF sets. It is not entirely clear why the lack of direction information would be affected by altitude.
  4. ^ There is considerable disagreement among references on who the Observer Centres reported to. Some illustrations show them reporting to the FCHQ, and this includes the description given by Bungay in the text. Others, including the image in Bungay, describe them reporting to the Sector Controls. This includes the RAF's own page on the system, as well as the wartime image found in this article. The later is likely because the ROC data is important during the attack phase, when the information needs to be relayed to the fighters as rapidly as possible. It is also possible they had links to both centres, switching as the battle progressed. The ROC center in Horsham may have also provided a middle-layer, collating reports and forwarding them to FCHQ.
  5. ^ The plotters were jokingly referred to as "the beauty chorus" and there are rumours commanders hand-picked the best looking women to run their ops rooms. The movie Angels One Five makes prominent mention of both.
  6. ^ The tote board is visible in the images, note the use of coloured lights to indicate the status of each "section" within the squadron. Squadrons typically had two or three sections, identified by colour codes.
  7. ^ Several all-time sunshine records were set during the summer of 1940.


  1. ^ Max Westley, "Pip–Squeak – The Missing Link", Duxford Radio Society Journal, Autumn/Winter (October) 2010
  2. ^ a b c d Ministry 1941, The British Fighter Force on Guard.
  3. ^ Winston Churchill, The Second World War, Volume 2, 1949
  4. ^ a b Burns, Russell, "The Evolution of Modern British Electronics, 1930-1945", Trans. of the Newcomen Society, 2006, p. 225.
  5. ^ a b c d e f g h Bungay 2010, p. 47.
  6. ^ a b Zimmerman 2013, p. 178.
  7. ^ a b Zimmerman 2013, p. 182.
  8. ^ a b Bowen 1998, p. 24.
  9. ^ Zimmerman 2013, p. 184.
  10. ^ a b Corrigan 2008, p. 5.
  11. ^ a b Zimmerman 2013, p. 186.
  12. ^ a b c d Corrigan 2008, p. 4.
  13. ^ a b Zimmerman 2013, p. 190.
  14. ^ a b c Coakley 1992, p. 30.
  15. ^ Zimmerman 2013, pp. 190-191.
  16. ^ a b c Bungay 2010, p. 49.
  17. ^ See images.
  18. ^ a b Zimmerman 2013, p. 191.
  19. ^ Westley 2010.
  20. ^ Price 1980, pp. 22–27
  21. ^ a b Ramsay 1989, pp. 14–28.
  22. ^ Coakley 1992, p. 29.
  23. ^ "Mr Baldwin on Aerial Warfare – A Fear for the Future", The Times, November 1932, column B. 11.
  24. ^ Robin Holmes, "The Battle of the Heligoland Bight, 1939: The Royal Air Force and the Luftwaffe's Baptism of Fire.", Grub Street, 2010, pp. 67-70.
  25. ^ Harry Butowsky, "Opana Radar Site", National Register of Historic Places, National Park Service, 10 March 1993
  26. ^ a b Zimmerman 2001.
  27. ^ Bungay 2010, p. 51.
  28. ^ a b c d Zimmerman 2013, p. 252.
  29. ^ Brimmicombe-Wood.
  30. ^ James Rothwell, "The weather during the Battle of Britain in 1940", Weather, April 2012, pp. 109–110.
  31. ^ Ministry 1941, Phase I.
  32. ^ a b Michael Korda, "With Wings Like Eagles: A History of the Battle of Britain", HarperCollins, 2009, p. 130.
Further reading
  • """Understanding The Dowding System. The Association of RAF Fighter Control Officers. 
  • "The Battle of Britain; August – October 1940". Battle of Britain 70th Anniversary. Royal Air Force. 

External links

  • The Filter Room - WW2 - Radar Command, WWII film on the role of the Filter Room.
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