Chain Home

Chain Home, or CH for short, was the name given to a ring of coastal radar stations built by the Royal Air Force before and during the Second World War. These stations were used to detect and track aircraft, giving early warnings of incoming enemy planes. It was the world's first early warning radar network and the first military radar system to become fully operational.

The idea for Chain Home began in late 1934 when the Tizard Committee asked radio expert Robert Watson-Watt to look into claims about radio weapons. His assistant, Arnold Wilkins, showed that while death rays were impossible, radio could be used to detect objects from far away. By February 1935, they successfully demonstrated this by detecting an aircraft using a simple radio setup.

By 1936, work began on building a production version of the radar. The first five stations, covering the area near London, were installed by 1937 and started full operation in 1938. Over the next few years, more stations were added, creating a network that could send information to fighter aircraft through the Dowding system.

Chain Home played a key role during the Battle of Britain in 1940. The radar systems could spot enemy aircraft while they were still forming over France, giving RAF commanders enough time to position their planes effectively. This help made the RAF's forces seem three times larger, allowing them to defeat bigger German groups. By the end of the war, over 40 Chain Home stations were in use, including mobile ones for overseas locations.

Development

Prior experiments

Since the early days of radio, signals have been used for navigation through a method called radio direction finding (RDF). RDF can find the direction of a radio transmitter, and by using several measurements, it can figure out a receiver’s location. The UK was the first to create a service using this idea, called the Orfordness Beacon.

Certain materials, like metal, can reflect radio signals. This made it possible to find the location of objects by sending out a signal and measuring the reflections. Early systems could only find the direction of objects, not how far away they were, so they were mainly used to warn about icebergs or collisions in bad weather.

Radio research in the UK

Since 1915, a scientist named Robert Watson-Watt worked at a lab connected to the National Physical Laboratory. He became interested in using radio signals from lightning to track storms but found the old methods too slow. In 1922, he invented a new way using a special tool to quickly find the direction of signals.

During this time, another scientist named Edward Appleton was doing experiments to measure the distance to layers in the atmosphere. Watson-Watt learned about these and started doing similar tests. This led to the creation of a new research station where Watson-Watt became an expert in radio technology.

Detection of aircraft

In 1931, a new scientist named Arnold Frederic Wilkins joined Watson-Watt’s team. He tested a new type of radio receiver and found that aircraft flying nearby changed the signal strength. This discovery set the stage for developing radar in the UK. Early systems could find the direction of aircraft but not their distance.

A big challenge was to find a way to measure distance. The solution was to use short bursts of signals and measure the time it took for them to bounce back. This allowed a single station to find both the direction and distance of an aircraft.

"The bomber will always get through"

In 1932, two important men, Winston Churchill and Frederick Lindemann, saw the fast growth of Germany’s aircraft industry. Later that year, another leader, Stanley Baldwin, gave a speech saying, “The bomber will always get through,” meaning bombers could always reach their targets.

In 1934, the Royal Air Force did exercises where bombers tried to attack London while fighters tried to stop them. The results were poor, with most bombers reaching their targets. This led to debates about whether Britain should focus on building more bombers or improving defenses. Some believed new fighter planes could stop bombers, while others wanted to build more bombers to attack first.

Tales of destructive "rays"

In the 1920s, some people claimed to have invented devices that could project energy over long distances, but these turned out to be fake. There were also stories about Germany developing new radio weapons, like rays that could stop engines or cause other damage. The British government took these stories seriously because, if true, such weapons could make bombers useless.

Tizard committee

Because of the need for better air defense, a group called the Tizard Committee was formed in 1934. They asked Watson-Watt to look into the idea of “death rays.” Watson-Watt and Wilkins calculated that the energy needed for such a ray was too high with current technology. Instead, they suggested using radio waves to detect aircraft.

"Less unpromising"

Watson-Watt told the committee that death rays were not possible but suggested that detecting aircraft using radio waves was more feasible. They needed to find out if this idea could work. Watson-Watt and Wilkins wrote a secret report explaining how they could use radio signals to detect aircraft. They calculated that with the right equipment, they could detect aircraft up to 10 miles away.

Daventry experiment

The committee gave money to test this idea. They used a BBC radio station in Daventry and a van with special equipment to receive signals. On February 26, 1935, they tested the system as an airplane flew over. They saw clear signals on a special screen, proving that aircraft could be detected using radio waves.

Experimental system

A scientist named Edward George Bowen joined the team and helped build a new radio transmitter and receiver. In May 1935, they moved the equipment to Orfordness for more testing. On June 17, 1935, the system detected an airplane landing nearby, marking the first successful use of radar.

Planning the chain

In August 1935, a scientist named Albert Rowe suggested calling the system “Radio Direction and Finding” (RDF). Watson-Watt planned to build a network of stations along the east coast of Britain to detect incoming aircraft. By December 1935, the government approved building five RDF stations, and work began quickly.

Into production

The system was built using existing technology to speed things up. Different companies made parts of the system, and the first five stations became operational in August 1938. By September 1938, they were fully running during a crisis in Europe.

Deployment

In 1936, tests showed that radar could help guide fighter planes to intercept bombers. By September 1939, when war began, there were 21 operational radar stations. After the Battle of France in 1940, the network grew to cover more of Britain’s coast.

Battle of Britain

During the Battle of Britain, some radar stations were attacked, but their strong towers survived. The German aircraft found them hard to destroy, so they stopped trying.

Upgrades

By 1942, newer radar systems took over many duties from the original chain. These new systems could scan a wider area and show a map of the airspace, making it easier to guide fighters. The original radar stations were upgraded with more powerful transmitters and new ways to measure distance and height.

Big Ben

When Germany started bombing Britain with V-2 rockets in 1944, these missiles flew too fast and high for radar to detect early. Some radar stations were changed to try to track the rockets during their flight, helping to warn people where they might land.

ROTOR

After World War II, Britain’s radar system was updated due to tensions with the Soviet Union. Some old radar stations were rebuilt to work better, and a new system called ROTOR was created. The very last of the original radar systems stopped working in 1955.

CH today

Some of the old radar towers still stand today, though most have been changed or removed. A few are protected as important historical buildings. One tower in Essex is still in its original condition and is listed as important. Other towers are used for different purposes, like training or communication.

Description

Chain Home radar stations were set up in pairs. One site held the towers that sent out signals, while the other, a short distance away, held the towers that received them. The system used tall steel towers arranged in a line, with antennas stretched between them to send out a strong signal forward.

Operators used special equipment to measure where the reflected signals came from. They would adjust antennas and note the strength of the signals to figure out the direction and distance of aircraft. This information was then shared with others who plotted it on maps to track the movements of enemy planes during the war.

Detection, jamming and counter-jamming

From May to August 1939, the LZ130 Graf Zeppelin II made flights along Britain’s North Sea coast. It investigated tall radio towers being built from Portsmouth to Scapa Flow. German reports say they noticed signals from the Chain Home radar but couldn’t prove it.

During the Battle of France, German forces noticed strange signals but didn’t know what they were. By mid-June 1940, they learned these signals came from radar stations along the English Channel coast. After the Battle of Dunkirk, when the British left a radar station in Normandy, German experts learned more about how it worked. Though they thought British radar wasn’t very good, they missed how important the whole system was, including how to report and use the information.

The British knew the Germans would try to block their radar, so they built ways to protect it. One way was to change the frequencies the radar used. They also had special tools to filter out unwanted signals. During the Battle of Britain, these tools helped the radar work even when the Germans tried to jam it. The British adapted quickly to German jamming attempts, keeping their radar effective throughout the battle. This helped British pilots spot enemy planes better than the Germans could.

Comparison with other systems

Chain Home was a simple system compared to others of its time. For example, the German Freya radar used shorter waves and a smaller antenna, making it easier to aim and use less energy. However, Freya could only see about half as far as Chain Home and could not tell the height of aircraft.

Chain Home was built using parts that were already available, which is why it used longer waves. It could see about 120 miles away, but it could not turn to watch all directions. This meant that once airplanes flew past it, Chain Home could not track them anymore. Later, new radars and special airplane equipment helped solve this problem.

Chain Home sites

Radar sites were placed all around the UK during the years 1936 to 1945 because technology was changing quickly and needs were different. By 1945, there were more than 100 radar sites in the UK. After the war, a project called ROTOR worked to organize these sites better.