A few anti-aircraft guns and searchlights were available to defend London. However by gun defences had been considerably strengthened and a number of Home Defence Squadrons had been formed. The B. He saw the aircraft lit up by searchlights and attacked by firing his machine gun into the underside of the airship until it caught fire. Despite carrying an inflammable gas, hydrogen, Zeppelins had proved hard to shoot down because, even if the bullets penetrated the gas balloon, there was no oxygen to support combustion. This was seldom the case because the airships flew high.
The development of a gun using incendiary bullets by mid played a part in improving the effectiveness of aircraft defences. Green of the Royal Aircraft Factory. It had a 70hp Renault engine giving it a speed of 70 mph and a peak altitude of 10,ft. In total some 3, aircraft of this type were built. This began on May and they saw first action in July.
However it was the highest scoring fighter in the first world war shooting down more German aircraft 1, than any other Allied plane. It was the first British fighter to have two propeller synchronised machine guns mounted side by side in front of the cockpit. It had a far better performance than the B. At the start of the war there was little experience of anti-aircraft gunnery.
In anti-aircraft gunnery was in its infancy and most of the deployed guns were field guns configured to fire upwards. It was a very limited force with only four batteries each of which was armed with four Vickers naval guns each mounted on an armoured vehicle. The Vickers gun could only fire four rounds a minute.
In the first design it had a limited range of 3, yards but improvements in ammunition progressively improved the distance the shells could travel. Three gun Batteries were used to defend central London. However, in a response to air attacks on London and elsewhere, the gunnery capability was greatly expanded and by June Britain had anti-aircraft guns, and searchlights in position to defend targets against possible German attack.
Initially gunnery was so inaccurate that Londoners did not have much confidence in it. It was estimated that it took 15, shots to down an aircraft at the start of the war but, despite the lack of kills, the gunfire forced the enemy to fly higher and, eventually, as gunnery and aircraft defences improved, to fly at night.
This was an optical coincident range finder 2 metres long on a tripod. It measured the distance to the target and the elevation angle, which together gave height. This greatly improved gunnery effectiveness. It was clear that a purpose built anti-aircraft gun was urgently needed. After trying a modification to a 3.
It was the first equipment designed specifically for the anti-aircraft AA role. This 3 inch gun mounted on a 20cwt vehicle was introduced in March It was a very effective gun and continued in service until the s. At 45 degrees it had a range of almost 11,yds with a rate of fire of 25 per minute and an effective AA ceiling of 23, ft.
This was sufficient to attack the Gothas that operated up to 16,ft. Early designers of AA equipments mounted their guns on lorries that were easily available but because they were difficult to stabilise they were soon replaced by towed platforms. As Gotha raids on London intensified, in mid a barrage of 30 of these guns was set up on the eastern approaches to defend London.
This had the effect of causing the Gotha to change tactics and concentrate on night time attacks. The Gotha and Giant night raids continued throughout , almost unscathed, until December when the defences began to have success with guns and the RFC, now equipped with the Camel, were increasingly successful in intercepting the Gothas at night. Rather late in the War the defence of London was enhanced by the use of barrage balloons.
They were deployed during and and they became an important element in the air defence system by constraining the freedom of attackers to use all the airspace. Each Apron consisted of three balloons yards apart joined together by a heavy steel cable. There is no recorded incidence of these balloons ever bringing down an enemy aircraft but they caused the enemy aircraft to fly in a smaller band of heights above 10,ft and thereby enabled the gun and aircraft defences to concentrate on these height bands.
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Furthermore the Gothas were forced into flying high thus reducing the accuracy of their bombing. This led to a reduction in the frequency of raids. In the absence of radar the home defence forces relied upon observers on the coast to warn of impending attack. The London Metropolitan Observation Service was established with about outposts. The service was staffed by policemen who used instruments to measure the bearing of the approaching aircraft and the angle of its course and report them to the Observation Service HQ at Horseguards, London.
This enabled the defences to be prepared. Guns could be ready and aircraft could be directed to intercept enemy aircraft. Of course, at night, it was difficult to see the aircraft and direct gunfire to them. Searchlights were used to help the gunners but it was difficult to ensure that the searchlight pointed quickly at the attackers. The searchlights were powered by electrical filament lamps or by acetylene gas hence were not very bright.
The electric arc lamp was not invented until Large hearing aids were used to locate attacking aircraft. The operator listened to the two horns separated horizontally and swung them around to determine the bearing of the target; then he used the horns separated vertically to determine the elevation of the target. Next he read off the elevation and the bearing and passed it to the searchlight operators and the gunners.
Frequently blind operators were used to man these equipments because of their superior hearing skills. Acoustic detection was also sometimes used by the Observer Service to provide some early warning of air attack. Some large sound collectors were cut into cliffs in Kent as an aid to early warning of airships and aircraft. Also concrete sound collectors were built by the Royal Engineers as part of an extensive Zeppelin and enemy aircraft detection system deployed down the East Coast of Britain. The sound of approaching aircraft was reflected off the concave 'mirror' surface and received into a trumpet mounted on a steel column.
The trumpet was connected to a stethoscope used by the operator or 'listener'. The part of the dish that produced the most sound indicated the direction of the approaching aircraft. However, after a few years, the War Office became concerned about the build up of forces by the French. In particular they had an Air Force of over aircraft whilst, in , Britain had only aircraft.
The politicians decided that Great Britain should have an Air Force at least as strong as that of any country that could attack us. These plans were developed to defend Great Britain from a potential air attack by the French. The aim of these systems was to match the French Air Force strength for strength. It was decided that the target strength was to be 35 bomber squadrons and 17 fighter squadrons.
This aircraft strength was originally to be supported by a force of guns with searchlight support. The plan was for central London to be defended by guns supported by searchlights with an outer belt of aircraft defences stretching around London, across the South of England and up to the Wash. An outer ring of guns was provided to break up enemy attack formations before they entered the aircraft fighter zone.
An extensive observer force named the Observer Corps was established in and a comprehensive communications network was developed. This was all brought together organisationally under the title of Air Defence of Great Britain. By it was realised that the French were not the main threat as Germany began to re-arm extensively. The plan was revised by restructuring the Aircraft and Observer belt to cover the east coast from Dover to the Firth of Tees and the south coast from Dover to Portsmouth.
The military were well aware that improved warning of the approach of air raids was needed. A plan was developed to improve the first world war sound alerting system and to use the noise made by approaching aircraft to give warning of an attack and thus provide an alert to the defensive forces. Large concrete sound collectors were built and installed on the South coast in Kent during the early s. These measured meters in diameter and on a quiet day could detect aircraft 20 to 30 miles away. This was some 20 miles before detection with the unaided ear and, as aircraft at this time flew at about mph, gave an early warning of some ten minutes.
In the early s the concrete sound collectors participated in the annual Air Defence exercises with the RAF. The picture above shows one such collector. The operators sat in the hut in the centre below the dish and they could use the acoustic probe seen reaching to the centre of the dish to detect and, to some extent, find the direction of aircraft. Because it needs a large collector to collect low frequency sounds efficiently it was decided to supplement the acoustic detectors with large walls measuring feet long and 26 feet high.
Initially these used purely auditory detection but later they were fitted with amplifiers and microphones to improve their sensitivity. The picture shows the detector built at Greatstone, Kent. In spite of the limitations of this sound sensor system it was originally intended to defend the south coast from Swanage to The Wash with the early warning provided by three ft walls in the Thames estuary and a further twenty one for the remainder of the coast.
It was also planned to have ten of the 30ft bowls installed in the estuary and four installed on the rest of the coast. The various sites were to be linked to defence headquarters by a telephone network. This plan was abandoned in after the early work on the newly discovered Radar had shown promise. The Sopwith Snipe was an improvement on the Sopwith Camel that had been widely used in WW1 as a fighter at home and abroad. It had a hp Bentley rotary engine which enabled it to fly faster mph and higher 19,ft than the Camel.
It was armed with the standard set of twin, front mounted, Vickers 0. They started service with the RAF in and stayed as the only home defence aircraft until , remaining in service until In March the RAFs first all metal fighter, the Armstrong Whitworth Siskin entered service and became the RAFs principal fighter of that period with a maximum speed of mph and a service ceiling of 21, ft. The Bristol Bulldog entered service in the UK in May and remained one of the most popular RAF fighters until , employed mostly for home defence.. With a top speed of mph it was a single-seat fighter capable of operating in day and night-time conditions.
It was armed with two 0. It was in this plane that Douglas Bader crashed and lost both legs after performing aerobatics. It was the first RAF plane to have a speed of over mph in level flight and was therefore 30mph faster than the Bulldog. It was highly acrobatic and could climb at over 2,ft per minute with a ceiling of 28,ft and was powered by a supercharged hp Rolls Royce Kestrel IIS liquid cooled engine, and was armed with two Vickers III Machine Guns. This design led on to the Hawker Hurricane which entered service in , and became one of the mainstays of the Battle of Britain.
The similarity of fuselage shape is clear but the Hurricane was the first monoplane fighter of the RAF. It was also the first with a retractable undercarriage and an enclosed cockpit. It was powered by a Rolls-Royce Merlin engine, and was capable of over mph with a service ceiling of 36,ft. It was armed with eight Browning machine guns in the wings.
You can think of a radar unit as a flash light. Instead of emitting visible light, radar emits invisible microwaves at a high frequency. The radar antenna sends out a short, high-power pulse of waves. When the waves hit an object, they echo from it and some power gets reflected back to the receiver. The time delay between the transmission and the receipt of the echo is used to determine the range of the reflector. Usually the same antenna is used to receive the much weaker signals that return but in the early days of radar a separate receiving antenna was used.
The width of the beam of radiation is set by the size of the antenna and the frequency of the microwaves. Larger antennas and higher frequencies produce narrower beams. This is used in scanning radars. In the early days of radar operators had to look hard at the radar displays to see if a target was detected and to follow the target on the screen as the target moved. This was a very tedious job and could make the system slow to react to new threats. In later years advanced signal processors were able to detect automatically and to track aircraft targets with no assistance from operators and this greatly speeded up the operation of the system.
In the early s the War Office were aware that the sound sensors only provided limited early warning and they sought new ways of detecting and disrupting air attacks. In February an experiment was conducted in which a Heyford bomber was flown though the beam of a BBC radio transmitter at Daventry whilst the received radio signal strength was measured. It was noticed that the received signal varied as the aircraft flew in and out of the beam.
Thus the principle of radar was discovered. Much further work over the next few years led to the installation, by the start of WW2, of a chain of radars from Ventnor on the Isle of Wight to the Firth of Tay.
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This radar chain played a vital part in the defences of Britain during the second world war. The picture shows the Ventnor radar site. Wires supporting dipole transmitter antenna elements were strung between the three ft tall towers to create an array aerial forming a horizontal fan shaped transmitter beam.
Battle of Britain
The four ft wooden towers shown on the right of the picture are used to support the receiver antenna. They are separated from the transmitter to prevent the high powered transmissions damaging the sensitive receiver. Transmissions were made at frequencies in the region of 20Mhz where the wavelength 15 Metres roughly matched the wingspan of the target aircraft. A detection range of miles was achieved with a claimed accuracy of one mile.
Effective though the Chain Home CH radars were, they suffered from the great disadvantage that they did not rotate hence it was difficult and slow for operators to determine the direction of the approaching aircraft and sometimes difficult to distinguish between a single aircraft and a multi aircraft raid.
It also was not good at detecting low flying aircraft. It operated at Mhz at a frequency ten times higher than that of Chain Home and had separate transmit and receive aerials. The aerials were not continuously rotated but, instead, were aimed at the target and moved from side to side to get the best reading of aircraft direction. CHLR The Radar was frequently mounted on the top of one of the ft CH transmitter towers to improve its low level coverage.
This was fully rotating and used a common aerial to transmit and receive. It operated at around Mhz and had a beam width of 15 degrees. With a peak power of some 80Kw it could detect a bomber at about 90 miles. To overcome the difficulty of sending signals to a rotating antenna some parts of the transmitter were attached to, and rotated with, the antenna.
This Radar was also capable of producing a good indication of the height of aircraft detected. It enabled controllers to direct fighters to intercept enemy aircraft by watching both aircraft on the radar display screen — a facility that came to be known as Ground Controlled Intercept GCI.
Early versions of this Radar were used in and later versions from to the end of the War. Initially it consisted of three hundred volunteers who were sworn in as Special Constables whose duties also included observation work and who worked in their spare time to spot aeroplane activity. However once war broke out it was realised that they could perform a very important function in supplementing the information provided by radar. The Corps played a vital role during World War II giving advance warning to Fighter Command of incoming enemy aircraft as well as plotting their position and movements.
The Corps volunteer members became highly skilled in the field of aircraft recognition as a result of this. By , over 1, OC posts had been established. Its manpower was greatly increased, eventually reaching a strength of 32, with over 1, observation posts largely on the south and southeast coasts. In it was renamed The Royal Observer Corps. The individual observer posts of three to five men would look and listen for the approaching raid.
The diagrams above show the main information flows. The information flow and aircraft control network was complex. Aircraft positions from the Chain Home Radars along the south and east coasts were passed to the local radar station where the detections of enemy aircraft were plotted on a map. When radar operators were satisfied that they had accurate data they passed the raid information, by telephone, to the filter room at Fighter Command Head Quarters FCHQ.
The filter room at FCHQ received aircraft and raid position reports from many radar sites. Here any ambiguities in the information arriving from the various radar sites linked to HQ Fighter Command were removed and operators created an air picture in which all the aircraft were placed into categories such as friendly, hostile and unidentified. At Group Headquarters commanders allocated tasks to sectors according to geographical position of the threat or the availability of defending fighters in the area covered by the sector.
Battle of Britain
The sector commanders then used information from local radar stations using the Chain Home Low Radar, information from the Observer Corps and information about the availability of aircraft resources to decide on the response to the threat. This response could employ gunnery, barrage balloons and fighter intercepts. In the early days of the war friendly aircraft returning from a mission could easily be confused with enemy attackers.
Friendly aircraft made themselves identifiable by responding to instructions by the controller to change course so that their radar blip moved accordingly. This used the pilot's radio to transmit a signal regularly so that the friendly aircraft could be located by the radio-frequency direction finding DF system. This position fix assisted the filter station in identification. As the war progressed better and better means for friendly aircraft identification were developed.
Eventually aircraft were fitted with transponders that reacted to interrogations from signals sent out from a supplementary radar attached to the main radar antenna. Ground Controlled Intercept could be used to direct aircraft to close proximity to the attackers but at night, or if visibility was poor, interception might still be difficult. Ideally radar is required on the fighter aircraft to assist the pilot to intercept the enemy aircraft. The aircraft entered service with this radar in January The radar antennas can be seen on the aircraft nose and on the wing tips.
This Radar had a fixed beam hence it produced a range indication but it could produce only crude directional information as the pilot swung the aircraft from side to side to optimise the signal, but it greatly assisted the Mosquito in homing in on the attackers. The Radar operated at a frequency of MHz.
The invention of the magnetron in by Randall and Boot at Birmingham University led to the development of Radars operating at 3Ghz 10cm wavelength and above. At these frequencies it was possible to have both a narrow beam and a small aerial. This enabled radar with small scanning aerials and narrow beams to be developed. Eventually a compromise was reached. On 13 August, Hitler agreed that the invasion front should to be narrowed, with the most westerly landing area being around Worthing.
The revised invasion plan was issued by the German High Command on 30 August. Hitler agreed that the invasion front should to be narrowed, with the most westerly landing area being around Worthing.
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The first assault wave was to secure the beachhead. The second wave packed the real punch for it was made up of two Panzer Divisions - each composed of tanks, artillery, mobile troops and Panzer grenadier assault infantry - and one motorised division. The role of the panzers was to break out of the beachhead and then sweep west towards Portsmouth. The first wave here was to consist of two infantry divisions, while the second wave was to include two Panzer Divisions that were to break out of the beachhead and advance north - to destroy the main reserves of the British army and establish crossings over the River Medway.
These landings were to be supported by parachute troops, who were to drop on the Downs above Brighton, to assist in the securing of the beach head for the Brighton-Worthing assault group, and north west of Folkestone in Kent to seize the Royal Military Canal of Napoleonic war vintage. The Germans saw this canal, which had been built to stop French invaders storming across Romney Marsh on their way to London, as a significant anti-tank obstacle that could, if not bridged, stall the advance of their panzers.
The initial objective for both assault groups was to establish a front from the Thames Estuary to Portsmouth. Then the build-up would begin with additional supplies and troops being brought in. When the build-up was complete the panzers of the Brighton-Worthing assault group would attack towards Basingstoke, Newbury and Oxford to secure crossing points over the Thames and to encircle and isolate London and the southeast in a great pincer movement. The remaining German forces, located around the Medway and on the Thames estuary, would then thrust towards London - the ultimate target of the invasion force.
The remaining German forces, located around the Medway and on the Thames estuary, would then thrust towards London General von Runstedt was in command of Army Group A, which was to be the main tool of invasion. As it happened, Von Runstedt had little faith in Halder's Sealion plan. He observed that Napoleon had failed to invade and the difficulties that confounded him did not appear to have been solved by the Sealion planners. Probably von Runstedt observed that one of the plan's main weaknesses was the small scale of the initial assault and the slow build-up. The first wave assault was to be carried out not by nine complete divisions but only their leading echelons numbering in each case around 6, men.
So only the equivalent of three divisions - around 60, men - would have been involved in the first wave assault. About tanks and very little artillery would have supported them.
An added factor worrying von Runstedt would no doubt have been the amateur and ad-hoc nature of the sea transport. The consequence would be troops landed at the wrong place or at the right place at the wrong time - or not landed at all if British sea and air power had not been completely destroyed. And these same problems of transport would apply to and slow down the build-up of reinforcements unless a number of major ports were captured quickly and intact - which was highly unlikely.
There were, said Hitler, other ways of defeating Britain. As Hitler started to back away from invasion the battle for dominance of the skies over England and the English Channel - a battle that now, perhaps, had little strategic value - reached a new peak of fury. On 3 September, with the RAF still far from destroyed, Field Marshal Keitel, head of the Armed Forces High Command, delayed Sealion until 21 September, and then again until 27 September, the last time the tides would be right before the end of the year.
The day after this last postponement was announced, Goering launched his final major offensive to destroy RAF Fighter Command in daylight action. It was a dismal failure, with the Luftwaffe losing twice as many aircraft as its potential victim. On 17 September - two days after Goering's defeat - Operation Sealion was postponed indefinitely.
The plan was never to be revived.
Hitler's attention was drawn increasingly to the east, and in June he invaded the Soviet Union. In Britain's defences against sea-borne attack were scaled down. By that date it was finally certain that the German army - fatally mauled in Russia - was in no position to invade Britain. But Britain's coastal defences were not dismantled. As the war ended, there were those who believed that the Soviet Union would be the next enemy and in anticipation of this NATO was formed in for the defence of western Europe and north America.
But even if the Soviets were the new enemy it gradually became clear during the early s that a Soviet invasion - if it came - would not be launched against the coast of Britain, and from coastal defences around the British Isles were gradually decommissioned. The Fortress Study Group. To give more prominence than I have given to measures contemplated, at one stage or another, by the Admiralty and naval Commanders-in-Chief for the reception of an invasion fleet that never sailed might have been misleading.
What shape would have been assumed by such naval actions as might have followed the sailing of that fleet, who can say? Perhaps the one assertion that can be made with confidence is that it would not have conformed to preconceptions which the wisest did not allow to take possession of their minds. In the outcome the issue of invasion or no invasion was decided not at sea but in the air.
It is conceivable that, if the Luftwaffe's attempt to gain air superiority over southern England and the English Channel had succeeded, Hitler might still have hesitated, as did his predecessors from Parma to Napoleon, to trust his transports to waters not commanded by his fleet. More probably he would have chanced his arm as he did in Norway, France and Russia.
What is certain is that the victory won by our air defences deprived him of all choice. While, therefore, I have given a good deal of my space to the enemy's preparations to land troops in this country and--with the proviso made above--to steps taken by the Royal Navy and Home Forces to oppose them, I have given still more to air attacks on the United Kingdom and corresponding measures of air defence.
If the Battle of Britain was not the most important action ever fought by British arms--and posterity may well deem it so--its effects were certainly no less momentous than those of the most striking victories of Hawke or Nelson. I have thought it right to review the battle in some detail, and no less desirable to sketch, against the background of political events, the period of preparation that began with the adoption of a scheme of air defence soon after the end of the First World War.
Strategically, the succession of night attacks on this country which began before the daylight battle was well launched and continued almost until the end of the war with Germany was less important. A German victory in the daylight battle might have made the United Kingdom indefensible; the night 'Blitz' and its aftermath never brought the enemy within sight of inflicting a decisive stroke.
But the raids had such profound and memorable effects on the fives of most of us that to slight them would have been a blunder. The flying bomb and the long-range rocket failed, in their turn, to bring much comfort to the enemy ; but their novelty, their challenge to the ingenuity of those called upon to assess and act upon the threat they offered, their potential value to an enemy more favourably placed than were the Germans by the time they brought them into use, all qualify them for much more than passing mention.
Some account of their early development seemed essential; and here I was fortunate in having access not only to much published and unpublished material about the rocket but also to new matter kindly laid before me by Dr. Fritz Gosslau, who was closely associated with the birth and progress of the rival weapon. Civil defence is the subject of a volume with that title, contributed by Major Terence H.
I have therefore made only brief references in my volume to civil defence matters,. Major O'Brien generously allowed me to see his book while it was yet unpublished; he also read the draft of some of my chapters and shared with me his knowledge of certain facts and figures of interest to both of us.
Unpublished documents have provided the bulk of my sources and have been placed unreservedly at my disposal. Detailed citation in a published volume of documents not generally available for study would serve no useful purpose even if it were desirable on other grounds; for the benefit of students who have access to the sources references are given in a limited number of copies which such readers will be able to consult. Nevertheless I must record here my particular debt to the authors of certain monographs and narratives prepared in the Cabinet Office Historical Section and the Air Historical Branch of the Air Ministry under the direction of Brigadier H.
Latham and Mr. Nerney respectively. Nerney and his staff have been indefatigable in searching the records on my behalf and he has given me much help and encouragement. For valuable comments and for checking certain facts and figures--for whose accuracy, however, I alone am answerable--I am grateful to Rear-Admiral R. Nerney and to many other officers and officials, some of them unknown to me, in various departments of the administration.
My task would have been impossible without the generous help of Mr. Brian Melland of the Cabinet Office and Squadron Leader Louis Jackets of the Air Historical Branch, who have sought out and translated or digested for my benefit a vast mass of material. I owe thanks, too, to others who have worked under their supervision, and in particular to Mr. I have had the advantage of receiving comments and suggestions from Commanders-in-Chief, Chiefs of Staff, members of wartime governments and other actors in my story who very kindly read my drafts in whole or part.
I cannot sufficiently express my gratitude to them for the generous gift of their time and special knowledge. Several of these commentators, and also some distinguished wartime leaders who had no opportunity of reading my drafts, were good enough to discuss points with me and give me the benefit of their experience. Such contributions did much to amplify, and sometimes correct, impressions drawn from documentary sources or from observation at a less exalted level.