'Enemy Sighted': The Story of the Battle of Britain Bunker and the World’s First Integrated Air Defence System

By Dilip Amin

Enemy Sighted is the story of the world’s first integrated air defense system and how the coalition of Hurricanes and Spitfires, Fighter Command’s Operations Rooms and Sector Stations, Radar Stations, Observer Corps posts, anti-aircraft gun and searchlight batteries, and balloon barrages, stood resolutely in the way of Operation Seelöwe, Hitler’s plan for invading Britain in the Summer of 1940.

Dilip Amin provides a fascinating insight into their development and eventual operationalization. The system provided a recognized air picture, giving everyone the same information at the same time, much like computers linked through the internet do today, except, in 1939 there was no computer and there was no internet!

Fundamental to its telling is the 11 Group Operations Room, today referred to as the Battle of Britain Bunker, and the people who worked there, deep below RAF Uxbridge. It was after visiting the Bunker that Churchill first uttered the immortal words, ‘Never in the field of human conflict was so much owed by so many to so few’.

Hidden underground, with its large map table and squadron display boards, and balloon and weather states, it is preserved as it was on 15 September 1940, the date celebrated as Battle of Britain Day. Dilip Amin describes how the Bunker operated, transporting the reader back to the time of the Battle of France and the final evacuation from Dunkirk. He guides the reader through the Battle of Britain, examining in detail, the events of 15 September, as seen by those in the Bunker and the combat reports of those flying the Hurricanes and Spitfires on that tumultuous day.

Finally, the book provides an insight into how the Bunker operated to protect Britain during the Blitz; support the exploratory raid on Dieppe; shield the troops landing in Normandy; and defend against Hitler’s V1 and V2 Vengeance Weapons. Enemy Sighted provides a compelling insight into the remarkable history of a secret Operations Room, that was pivotal within a world leading air defense system, and without which, an Allied victory in the Second World War would have been far from certain.

• Language: English
• Publisher: Pen and Sword
• Release date: Nov 30, 2023
• ISBN: 9781399049320

Dilip Amin

DILIP AMIN is a retired police chief superintendent, with a life-long interest in military history, military aviation, and the Royal Air Force during the Second World War. He volunteers as a tour guide at the Battle of Britain Bunker and relishes the opportunity to share its rich and fascinating story with visitors, bringing its history to life as a tribute to those who served there during the dark days of war. He now puts the investigative and presentational experience gained while in the police to good use, devoting much of his time to researching and writing about his field of passion.

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Introduction

This is the story of how Britain developed the world’s first integrated air defence system, and how that avant-garde framework was skilfully wielded to thwart invasion over eighty years ago. Fundamental to its telling, is the 11 Group Operations Room, commonly referred to as the ‘Battle of Britain Bunker’, and the people who worked there, deep below Royal Air Force Uxbridge. Without their involvement, Fighter Command’s pilots could not have routed the Luftwaffe during the Battle of Britain, and so would have been unable to prevent Operation Seelöwe or Sealion, the German invasion of Britain. If the Nazis had been permitted to land on British soil, then no doubt its people, inspired by their wartime leader Winston Churchill, would have fought stoically on the beaches and on the landing grounds. However, Hitler’s army, the German Heer, was not only vastly superior in numbers, but also possessed more heavy armament than the British, who had been forced to abandon much of their equipment in France. If Britain had been subjugated, then the course not only of British, but also world history, would likely have been reconstructed. It is therefore difficult to overstate how important the Bunker’s role was in frustrating the Nazis’ obsession of creating a Third Reich, and their appetite for world domination.

The Führer had declared that before invasion could take place, ‘The English Air Force must be beaten physically and morally to a point that they cannot put up any show of attacking force worth mentioning.’¹ To bring this about, the Luftwaffe needed to gain air superiority over the English Channel and intended landing grounds. The battle would therefore be predominantly fought over London and south-east England. It was the area covered by the Bunker, and it would come to be known as ‘Hell Fire Corner’. At its closest point, between Dover and Calais, the stretch of water separating Britain and Nazi Occupied France is just under twenty-one miles (thirty-three km). I have been privileged to fly in a Spitfire over the White Cliffs of Dover and can attest to the fact that the French coastline can clearly be seen from Dover. The distance, in aeronautical terms, really is extremely short, capable of being traversed by German aircraft in around five minutes.

It was for this reason that the greater part of the Hurricanes and Spitfires involved in the fighting during this conflict were controlled from the Bunker. They would shoot down over 1,300 of the 1,733 enemy aircraft claimed destroyed during the battle. Their contribution not only helped Britain to survive during the early part of the Second World War, but also ensured that it could, in due course, be used as the springboard from which to launch Operation Overlord, the assault on Hitler’s ‘Fortress Europe’. Indeed, it was having visited the Bunker, when the Battle of Britain was at its height, that stirred Prime Minister Winston Churchill to declare he had ‘Never been so moved’, and first utter the immortal words: ‘Never has so much been owed, by so many, to so few.’

With the advent of powered flight at the turn of the twentieth century, Britain was no longer an island in the sense that the sea was no longer an absolute barrier to invasion. The Royal Navy could not, on its own, be expected to guard against future incursions. Aircraft approaching Britain would be flying within a vast three-dimensional domain, making the task of detecting and intercepting them more difficult than was the case with ships. This is because only knowledge of two dimensions, both existing on a horizontal plane, is required to detect and intercept ships. The first is the direction from which they are approaching, the azimuth angle on the horizon, which is described in degrees. The second is their distance from the defending forces, the length of which is described in miles and feet, or kilometres and metres. Aircraft travel along these two dimensions, plus an additional third dimension on a vertical plane – height. If their height is unknown, then they cannot be successfully intercepted. A further challenge, in the case of aircraft, is a significantly reduced period in which to detect and intercept them. This is because they are travelling much faster than ships, and unlike ships they do not stop on reaching the coast, but instead continue their journey inland, at speed.

The challenge, therefore, was to create a system capable of detecting approaching enemy aircraft early enough to alert ground defences, and get fighter aircraft not only into the air, but also to the right place and at the right height. The solution was neither straightforward, nor immediate. Like in the Battle of Britain, which in reality was won by the ‘many’, and not the ‘few’, there were ‘many’ without whom the system would not have been realised. However, if credit is to be given to one individual, then that person is Hugh Caswall Tremenheere Dowding, who, as Air Member for Supply and Research and then for Research and Development, helped to oversee its development, and then as Air Officer Commanding, Fighter Command, directed its use during wartime. It is in recognition of this contribution, that the integrated air defence system is more simply and widely referred to as the ‘Dowding System’.

The system of air defence was integrated, meaning that for it to operate successfully, all elements were essential, and all needed to operate in unison. The aim was to develop a shared understanding of what was happening, in other words to develop a ‘recognised air picture’. So for example, the Senior Controller, sat sixty ft (eighteen metres) below ground at Uxbridge, to the west of London, was able to track German raiders as they crossed the English Channel, and could metaphorically ‘see’ when they approached Dover, some eighty-three miles (133 km) away. He had before him information on the raid’s direction of travel, height, strength and even whether it was composed of bombers, fighters, or both. He would be cognisant of the prevailing weather over Dover and even how high the barrage balloons were. It was as if he was looking out of the window, allowing him to make informed decisions on how best to deploy his finite resources. This was all possible due to an arrangement of teleprinter, telephone and radio telephony networks, established across the entire system. To those of us today, in the era of interconnected computers, this would appear unremarkable, let alone extraordinary, but we need to remind ourselves that this achievement was even more exceptional in a world without computers, or the internet.

There were six essential elements within the integrated air defence system. The first element was formed by the fighter aircraft that were directed to intercept enemy raids. The majority of these were Hurricanes and Spitfires; second was Fighter Command itself, providing a fighter control network through an organisational infrastructure of Sector and Satellite airfields or aerodromes, and Operations Rooms at Headquarters, Group and Sector level; third were the Chain Home and Chain Home Low Radio Detection and Ranging (Radar) stations. The ‘all seeing eye’ that informed Fighter Command, as to when and where the raiders would attack; fourth was the Observer Corps, whose members monitored and reported on the composition and movement of enemy raiders once they had crossed the coastline. They performed a vital role by mitigating Radar’s weakness at that time, which was the inability to detect aircraft once they had flown overhead and were continuing over Britain itself; fifth was Anti-Aircraft Command, whose anti-aircraft guns protected Britain from the ground, and whose searchlights exposed enemy aircraft prowling in the night sky; and lastly, Balloon Command, which offered protection at strategic locations and to vulnerable targets, by hindering the enemy’s ability to carry out low-level attacks.

By coming together, these individual elements all combined to present an immediate and unified response when faced with threats from the air. Radar detected enemy aircraft, often as they were gaining height over Northern France, and so provided early warning of an imminent raid. The information from Radar stations would be passed to the Filter Room at Fighter Command Headquarters, where it was ‘filtered’, or tidied up, before being shared across the system. As enemy aircraft crossed the British coast, their location, direction of travel, height and strength were reported on and shared by the Observer Corps. Details of raids entering 11 Group’s area were passed on to the Bunker at Uxbridge, from where anti-aircraft guns, searchlights, balloons and fighter aircraft were alerted and deployed.

As well as denying the Luftwaffe the air superiority it needed to invade Britain, what is perhaps less well known is the significant role performed by the Bunker, during some of the other major campaigns and engagements of the Second World War. The decisions made here helped slow down the Nazi invasion of France and the Low Countries; protected the embattled troops being evacuated from Dunkirk; supported the exploratory raid on Dieppe; shielded the troops landing in Normandy; and defend against Hitler’s Vergeltungswaffen, or Vengeance Weapons, the V1 and V2. These moments would influence not only British, but world history, and they are deservingly acknowledged in this account.

This book takes the reader from a time when Britain was subjected to attacks purely from the sea, to when the threat emanated from both sea and air. This fundamental shift in how the threat presented itself necessitated the creation and implementation of a new and radical system of defence. An exploration follows of not only what this new system was, but also how it was created, and how it was effectively deployed. Central to the operating of this system, was the 11 Group Operations Room at Uxbridge, or, as it is more commonly referred to today, ‘The Battle of Britain Bunker’.

Chapter 1

An Evolving Threat

‘Britain is No Longer an Island’

The Operations Room at Fighter Command’s 11 Group Headquarters was pivotal to Britain’s defence, at a time in its history when a malevolent foreign power, Nazi Germany, attempted to conquer and subjugate it. But why was it considered necessary, even before that conflict, that this island kingdom needed to be defended against the threat of attack? What evidence was there that Britain could, or would, be invaded by forces from beyond these shores? To understand the threat, we need to examine Britain’s past and ultimately how the sea, a natural barrier, was to become superfluous and made redundant by advances in aviation technology.

Hostile armies and large raiding parties have attempted to invade the British Isles throughout history. In some instances, they were able to land successfully on these shores, and on other occasions, they were comprehensively repulsed. In the year 55 bc, Emperor Julius Caesar landed with an army in Thanet, Kent, on the south-east coast of Britain, ushering in almost 400 years of Roman rule. Then, between 793 and 1066, marauding Vikings from Scandinavian countries repeatedly carried out raids along the north and east coast of Britain.

In 1066, King Harald Hardrada of Norway landed with an army on the east coast of Britain and fought King Harold of England, at the Battle of Stamford Bridge. Having defeated the invading army, the English King then travelled south to engage with William, Duke of Normandy, who had landed with his army in Pevensey Bay, Sussex, on the south-east coast. King Harold was killed at the Battle of Hastings and the Normans went on to rule England for over half a century.

In 1545, King Francis I of France ordered the French fleet to invade Britain, but its attempt to land on the south coast at Portsmouth was thwarted by King Henry VIII’s navy, led by his flagship Mary Rose. Unable to land in mainland Britain, the French then invaded the Isle of Wight and landed successfully at St Helens, Bonchurch and Sandown, where they remained until they themselves were vanquished by the English defenders.

An armada sent in 1588 by King Philip II of Spain, against Queen Elizabeth I of England, was defeated at sea by the English navy, led by Sir Francis Drake. This victory prevented the invasion army, which was waiting in Calais, from embarking and crossing the English Channel. On this occasion, a network of beacons positioned at high points along the coast were lit to warn the English defenders of an impending invasion, and for them to mobilise their response. This ‘chain’ of highly visible fires represented a fledgling system, being used to give early warning of an attack from the sea. During the Battle of Britain 352 years later, the British Isles would again rely on a ‘chain’ system of Radar masts and observation posts to provide early warning of an attack, not from the sea but from the air. It is noteworthy that the crest of the Royal Observer Corps, which played such a pivotal role in the defence of this country during the Second World War, honours its predecessors by depicting an Elizabethan Coast Watcher, in breastplate and helmet, holding a flaming torch in his raised right hand, and using his left hand to shield his eyes. He is standing on a cliff next to a flaming beacon, against a background of sea and a coastline with beacons. The central relief is surrounded by a pale blue enamel border, on which the motto Forewarned Is Forearmed is etched in silver.¹

In 1688, a Dutch army led by William of Orange successfully landed in Devon, on the south coast of Britain, and marched on London. The invading fleet was many times larger than the Spanish Armada, which had attempted an invasion 100 years before. The Dutch were able to land because of the support given to them by several English peers, in what would come to be known as ‘the Glorious Revolution’. Was this an invasion, or was it an invitation?

In 1797, the newly formed French Revolutionary Government, ‘the Directory’, sent an invasion force of 1,400 men, under the command of an Irish American, Colonel William Tate. The original plan was to land at Bristol, but adverse weather meant the invading army landed near Fishguard in south-west Wales. Many of the invaders were convicts who had been recruited for the task, and soon the rabble became drunk and unwilling, or incapable, of fighting. Such was the situation that a local cobbler’s wife, Jemima Nicholas, armed only with a pitchfork, detained twelve of the invaders by herself, and the remaining invaders surrendered to a local militia force within two days of their landing.

In 1805, Admiral Horatio Nelson’s British fleet defeated the French and Spanish fleets at Trafalgar, off the coast of Spain. This British victory denied the French Emperor, Napoleon Bonaparte, control of the English Channel, and so thwarted his plans for invading the British Isles. Britain would, as a result, maintain dominance of the seas for the next 100 years, and thereby possess the means to protect herself against attacks launched from foreign shores.

Regardless of whether these assaults on the British Isles had been successfully realised or not, they all shared two features from which lessons could be learnt and applied to address future maritime and airborne threats.

The first is that to engage aggressors and successfully repel them, either at sea or after they have landed, an attack must be identified at the earliest opportunity, and communicated speedily and effectively across the defending force. Meeting this requirement would become more challenging when facing threats from the air, where aircraft, unlike ships on the surface of the sea, could travel and, importantly, hide, in a three dimensional domain at any given height on a vertical plane stretching many thousands of feet.

The second, is that Britain was an island. The invaders in every case had needed to successfully navigate a body of water to reach Britain, and the only means of doing so had been by using seaborne craft, or ships. Ships had also been used defensively against attacks, and from the sixteenth century, the Royal Navy possessed a formidable array of seaborne craft … Britannia did indeed rule the waves. However, when Britain became accessible by aircraft, it became no longer an island in an aeronautical sense, and therefore the Royal Navy alone was not enough. Britain needed to defend herself against the evolving threat from aircraft. She needed an air force, with an array of aircraft operating within an integrated air defence system, in order to detect intruders and successfully challenge any incursion.

In 1908, the Daily Telegraph newspaper reported on the Royal Aero Club’s annual dinner, held at the famous Ritz Hotel, in London, with the headline, ‘Airship squadrons. Peril of the future’. The Duke of Argyll had referred to the ‘necessity of considering the possibility of having every part of a country visited and inspected by transient visitors who might or might not have hostile intentions’, and ‘the precautions that needed to be taken against intrusions by aeroplanes’. It was in response to this, that Charles Rolls, who had entered into partnership with Henry Royce, said that ‘England was no longer an island and that to maintain her supremacy she must now not only have the command of the sea, but that of the air as well.’²

Then, in 1909, an event occurred that would transform the nature of any threat which Britain was likely to face in the future. Lord Northcliffe, founder and proprietor of the Daily Mail newspaper, had issued a challenge the year before, offering a prize of £1,000 to the first person to fly across the English Channel.³ On 25 July 1909, Louis Blériot attempted the crossing in a fragile plane he had constructed from ash and cloth, and which was held together by piano wire. The machine’s modest 25hp engine could produce only a fraction of the power generated by a typical push-along garden lawnmower today. The flight, over some twenty-five miles (forty km) of water, between the port of Calais and the port of Dover, was completed in thirty-seven minutes. This achievement was a monumental landmark in aviation history, one worthy of Neil Armstrong’s words sixty years later, when he flew to the Moon: ‘one small step for man, one giant leap for mankind’. It demonstrated man’s ability to use machines to travel through the air, thereby circumventing the natural barriers of land and sea. These thirty-seven minutes had shown that Britain could be reached more rapidly and less conspicuously. There was now an added sense of renewed urgency to the threat prophesied by Argyll and Rolls, some seven months earlier.

The Literary Digest made an ominous prediction that, ‘If one machine bird can migrate from the continent to the island kingdom, why not 10,000?’ As if to support this premonition, it also reported on the congratulatory telegram sent to Blériot by Lord Roberts, Commander in Chief of the British Army, in which he stated: ‘It is impossible to imagine the far reaching effects of the feat. It may lead the way to great changes in the conduct of future wars.’⁴

Only five years after Blériot’s historic crossing, the country found itself embroiled in ‘The Great War’. Mainland Britain was attacked from the air for the first time on the morning of Christmas Eve 1914, when a German Friedrichshafen FF29 seaplane dropped four 4 lb (2 kg) bombs over Dover. The raid caused only minimal damage and minor injuries to civilians, but it had a disproportionate effect on the national psyche, creating a sense of helplessness and fear among the British public.

Lord Roberts’ forewarning of ‘great changes’ being necessary was proven to be correct, and the island kingdom deliberated on how best to defend itself against future aerial attacks from German airships and bombers … the threat had evolved, and so too would the response.

Chapter 2

A Three Dimensional Challenge

‘To Catch a Fly’

The evolving threat from the air greatly complicated Britain’s ability to defend itself from attack. Observation posts in isolation were no longer a sufficient means of surveillance, and the race was on to find and implement a more commensurate, integrated system of air defence. In order to understand the challenges of defending against air attack, we need to think about it in terms of space and time.

This view was affirmed in instructions issued to Fighter Command Controllers during the Second World War:

To meet enemy aircraft in the air, other than by purest chance, fighter aircraft must have the guidance of a Controller to direct them in space and time into the enemy’s vicinity. The Controller must know the position of the enemy in space and time; know the position of his fighters in space and time; and have the means of communicating with his fighters in the air.

This is the essential control in the air, for which the whole Fighter Operational Control System is designed.¹

It is appreciated that enemy aircraft can occupy any one of an infinite number of positions in the sky, which is a vast three-dimensional domain. They are almost always likely to have an intended target, which can be approached from different directions, on a horizontal plane, and different heights, on a vertical plane. If defending fighter aircraft, or ground-based anti-aircraft artillery are successfully directed to a precise position within a horizontal plane, currently occupied by enemy aircraft, they may still fail to make contact if they are not at the same height as the enemy, its position on a vertical plane. Both horizontal and vertical planes are attributes of the element defined as space. In addition, the defending aircraft or ground-based anti-aircraft artillery, will always aim to intercept the enemy aircraft before they reach their target, so they need to know precisely where the enemy is at any given moment, and therefore when the interception can be made, this is the element of time.

To help understand the challenge of effectively locating, and successfully intercepting enemy aircraft, entering territorial airspace, we can use the analogy of a spider catching a fly in a room, where the former is synonymous with the defender, and the latter, the intruder.

The spider needs to spin a web in order to catch the fly. It does this intuitively, regarding both the fly’s likely position within a room, on a horizontal plane, and how high its prey is likely to be flying, its position on a vertical plane. Both these two planes represent the element of space. By spinning a web in a suitable location, it will hope to get lucky and snare its prey. The spider does not need to know where the fly is at all times, it only needs to know when the fly becomes ensnared in the web, at which point the vibration will alert the spider and allow it to attack, this is the element of time. Unlike the spider, however, defending fighter aircraft or ground-based anti-aircraft artillery need always to be alerted and aware of the ‘fly’ while it is in the ‘room’. The ‘web’, that needs to be spun to effectively locate and successfully intercept enemy aircraft, therefore needs to cover the entire ‘room’, which in reality would encompass both the vast territorial airspace being defended, and adjoining airspace likely to be used by the enemy when approaching it.

The position of the enemy in ‘space and time’ was not readily gaugeable at the outbreak of the First World War. Radar had not yet been developed, and so Britain was unable to gain early warning of an attack. Its ability to effectively direct defending fighters and communicate vital information immediately, across all parts of the defence system, was rudimentary.

Existing facilities such as railway stations, military camps, police stations and lighthouses were engaged as ‘reporting posts’, to provide limited early warning of any possible raid on London. Not all these locations were equipped with a telephone, and messages would have to be relayed by a runner to another site, from which the information could be forwarded. All reports eventually led through to a central administration point at the Admiralty, and then had to be translated into instructions for the most appropriate airfields.²

The only option available to sight the enemy as they entered British airspace, was to mount permanent ‘standing patrols’, in which defending aircraft would fly along the English Channel and North Sea coast, hoping to see the attacking aircraft. This was costly in terms of resources and tactically flawed, because if defending aircraft had used most of their fuel by the time they spotted the enemy, then they were not able to engage them.

To compound the problem, there was insufficient coordination between the Royal Flying Corps (RFC), which was under the direction of the Army, and the Royal Naval Air Service (RNAS), both of which were involved in defending Britain against aerial attack. The RNAS claim that defending Britain against invaders had always traditionally been a naval responsibility was refuted by the RFC. This infighting led to a great deal of antagonism between the two arms of the military, resulting in a diminution of their collective capability to provide aerial defence. The issue was resolved for the time being, when responsibility for combating the threat from the air was ceded to the British Army in February 1916.

The challenge of defending against the aerial raiders became more pressing as the attacks intensified. By the end of 1916, German Zeppelin airships had killed 500 civilians, and 17,000 servicemen had been diverted from other duties to deal with the raiders. In the summer of 1917, long-range German Gotha bombers struck London, killing and wounding nearly 600 people in the initial raid. The fear felt on the streets spread upwards.³

During three raids in July 1917, over 120 British fighters took to the air over London to challenge German Gotha GIV bombers of ‘The England Squadron’, but only one defending aircraft was able to find and shoot at the raiders.⁴ Britain was shown to be woefully inadequate in defending its capital, and the Prime Minister, Lloyd George, commissioned General Jan Smuts to lead an inquiry to examine two distinct but interdependent issues: ‘The defence arrangements for home defence against air raids’, and ‘The air organisation generally and the direction of aerial operations.’⁵

In the first part of the report, Smuts identified that ‘no system of unified command in the air existed’, with little or no coordination, and ‘because of the fragmentation of command and the importance of the London anti-aircraft guns that a senior officer be appointed’.⁶ The recommendations were approved and Brigadier General ‘Splash’ Ashmore was recalled from France ‘to work out schemes of air defence for this area’.⁷ This scheme would form the catalyst of the world’s first integrated air defence system.

In the second part of his report, Smuts addressed the issue of air organisation generally and the direction of aerial operations. He recommended that an Air Ministry be created, to oversee Air Staff who would be responsible for the working out of war plans, the direction of operations, the collection of intelligence, and the training of Air personnel. In addition, he proposed that the Air Ministry and its staff proceed to work out the arrangements necessary for the amalgamation of the RNAS and RFC.⁸ This resulted in the formation of the Royal Air Force, which was inaugurated in April the following year, a move which would ensure that Britain’s ability to defend itself