Chain Home (AMES Type 1) Radar Stations – July 1940

• Number of operational stations: 22
• Operating frequency: 22–30 MHz
• Wavelength: 10–13.5 metres
• Power output: 200 kW
• Maximum detection range: up to 120 miles (192 km) at high altitudes

Chain Home Low (AMES Type 2) Radar Stations – July 1940

• Number of operational stations: 30
• Operating frequency: 200 MHz
• Wavelength: 1.5 metres
• Power output: 150 kW
• Maximum detection range: up to 50 miles (80 km) at low altitudes

Image: Chain Home radar installation at Poling, Sussex, 1945

The Vision of Sir Robert Watson-Watt

The development of Britain’s radar defences owed much to the vision and leadership of Sir Robert Watson-Watt, a Scottish physicist whose work in the 1930s played a central role in transforming theoretical radio science into a practical system of air defence. In 1935, while working for the Air Ministry’s Radio Research Station, Watson-Watt was asked whether it might be possible to create a so-called “death ray” capable of destroying enemy aircraft using radio waves. He dismissed the idea as impractical, but proposed a far more viable alternative: detecting aircraft by means of reflected radio waves.

On 26 February 1935, Watson-Watt and his colleague Arnold “Skip” Wilkins carried out a successful demonstration of this principle near Daventry, using a BBC shortwave transmitter. A Handley Page Heyford bomber was detected through the reflection of radio signals, confirming that aircraft could be located at a distance using this method. Known as the Daventry Experiment, this trial provided the first practical proof that radio detection of aircraft was feasible and directly led to the rapid development of operational radar.

From this point, progress accelerated under the direction of Watson-Watt and a growing team of scientists and engineers, including Edward Bowen and A.P. Rowe. By 1936, an experimental radar station had been established at Bawdsey Manor on the Suffolk coast. Over the following years, this work expanded into a network of fixed early-warning stations—later known as Chain Home—constructed along Britain’s eastern and southern coastlines. By the outbreak of war in September 1939, the core of this network was already operational, and it continued to expand and improve into 1940.

Radar’s Role in Britain’s Air Defence System

Radar—referred to at the time as Radio Direction Finding (RDF)—formed a vital component of Britain’s air defence system. The term “RDF” was intentionally misleading, adopted for security reasons to obscure the true nature and capability of the technology. In practice, it allowed the RAF to detect incoming German aircraft while they were still over the Channel, providing critical early warning.

Chain Home stations transmitted powerful radio pulses from tall steel masts. When these signals struck aircraft, a portion of the energy was reflected back and received by separate aerials, allowing operators to determine the approximate range and bearing of approaching formations. While not highly precise in isolation, this information was sufficient to track large enemy raids at considerable distances.

The system was most effective against aircraft flying at medium and high altitudes, where detection ranges were greatest. However, low-flying aircraft presented a greater challenge, particularly at longer ranges. To address this limitation, a complementary system known as Chain Home Low (CHL), or AMES Type 2, was introduced. Operating on shorter wavelengths, CHL stations were better suited to detecting aircraft at low altitude, including those attempting to approach beneath the main radar coverage. By the summer of 1940, an increasing number of these stations were operational, providing more complete coverage across a range of altitudes.

German Attacks and Miscalculations

The prominent radar masts along Britain’s southern coast did not escape the attention of the Luftwaffe. On 12 August 1940, as part of the opening phase of intensified operations against Britain, German forces launched coordinated attacks on several radar stations in Kent, Sussex, and on the Isle of Wight. These raids represented a deliberate attempt to disrupt Britain’s early-warning system.

A number of stations—including those at Rye, Pevensey, Dunkirk, and Ventnor—were attacked. While damage was inflicted in several cases, most stations were able to resume operation relatively quickly, as the steel lattice towers themselves were difficult to destroy and critical components were often housed in more protected structures. At Ventnor, however, the transmitter was put out of action, temporarily reducing radar coverage over part of the Channel.

Despite this, the overall impact of the attacks was limited. The robustness of the system, combined with overlapping coverage and rapid repair efforts, meant that Fighter Command’s early-warning capability was never critically degraded for an extended period. In addition, mobile radar units and adjustments within the wider system helped to mitigate temporary gaps in coverage.

Although German intelligence was aware of the existence of these installations, it did not fully appreciate their importance within Britain’s air defence network. A minority of Luftwaffe signals officers recognised their potential significance, but this understanding did not translate into a sustained operational priority. Attention soon shifted toward attacks on RAF airfields and infrastructure instead.

This proved to be a significant misjudgment. The radar network remained largely intact throughout the critical phases of the battle, continuing to provide the early warning upon which Britain’s defensive system depended.

Radar in Action: 15 August 1940

The value of radar was demonstrated with particular clarity on 15 August 1940, a day on which the Luftwaffe launched large-scale attacks against Britain from multiple directions. German planners, believing that northern Britain was only lightly defended, committed formations from Norway and Denmark to strike targets in the north-east, while simultaneous raids were directed against southern England.

These incoming formations were detected at long range by Chain Home stations, including those along the east coast. Radar plots revealed the scale, direction, and approximate altitude of the raids, allowing Fighter Command to recognise that the attacks were not isolated incursions but part of a coordinated effort. This information was passed through the Filter Room at Bentley Priory and on to the relevant Group and Sector Operations Rooms.

As a result, fighter squadrons in northern England were able to scramble in good time and position themselves effectively to intercept. Aircraft of 13 Group, which might otherwise have been caught unprepared, were directed to meet the incoming bombers and their escorts before they could reach their targets. The German formations, expecting limited resistance, instead encountered organised and determined opposition, suffering significant losses.

At the same time, radar coverage in the south ensured that 11 Group was not misled into committing all of its resources prematurely. The system allowed for a measured and proportionate response across multiple sectors, preserving strength where needed and avoiding unnecessary deployments. In this way, radar contributed not only to interception, but to the overall balance and efficiency of Britain’s defensive effort on one of the most demanding days of the battle.

Radar and the Dowding System

Radar’s true effectiveness lay not simply in detection, but in its integration into a wider system of command and control. This network—developed under the direction of Air Chief Marshal Hugh Dowding—is commonly referred to as the Dowding System, the first fully integrated modern air defence system of its kind.

Information from Chain Home and Chain Home Low stations was transmitted to the central Filter Room at Bentley Priory, where reports were assessed, filtered, and consolidated. From there, the data was passed to Group and Sector Operations Rooms, where it was combined with visual reports from the Observer Corps and interpreted by controllers.

This process enabled Fighter Command to build an accurate and continuously updated picture of incoming raids. Crucially, it allowed for the efficient use of limited fighter resources. Squadrons could be scrambled at the right moment, directed to the correct altitude and position, and committed only where needed. This avoided unnecessary patrols, conserved fuel, and maximised the effectiveness of interceptions.

Without radar, Britain’s air defence would have relied far more heavily on visual observation alone, significantly reducing reaction time and limiting the ability to intercept enemy formations before they reached their targets.

Summary

Radar was not a weapon in the conventional sense, but it was one of the most important force multipliers available to Britain in 1940. Through the work of Watson-Watt and his colleagues, and its integration into the wider command structure devised by Dowding, it provided Fighter Command with a decisive operational advantage.

While radar alone did not determine the outcome of the Battle of Britain, it was an essential component of the system that enabled victory. By providing early warning, improving coordination, and allowing for the effective deployment of limited resources, it ensured that the RAF could meet repeated German attacks with a level of organisation and efficiency that the Luftwaffe never fully matched.