In the summer of 1940, outnumbered RAF fighter pilots kept turning up in exactly the right place to meet the Luftwaffe, again and again. To the Germans it looked like uncanny luck. It was nothing of the sort. Along the coast of Britain stood a line of tall steel towers, and behind them an invisible machine of wood, wire and human discipline that could see the enemy coming while he was still forming up over France.
That machine was radar, and the network built around it. More than the Spitfire or the Hurricane, it may have been the single most important reason Britain won the Battle of Britain.
Quick Facts: Chain Home & the Dowding System
- What: The world’s first integrated early-warning radar network
- Key figure: Robert Watson-Watt; proven at the Daventry Experiment, 26 February 1935
- Towers: Transmitter masts around 360 feet tall
- Range: Roughly 100 to 120 miles out to sea
- The system: The Dowding System, run from Bentley Priory
- Speed: Detection to fighters scrambled in about four minutes
The Daventry Experiment
Radar began, oddly, with a question about a death ray. In 1934 the Air Ministry asked the Scottish physicist Robert Watson-Watt whether radio waves could be used as a weapon to destroy aircraft. They could not, he concluded, but the reflected waves could be used to find aircraft. On 26 February 1935, near Daventry, his colleague Arnold Wilkins used the reflections from a BBC shortwave transmitter to detect a passing Handley Page Heyford bomber. The principle was simple: send out a pulse, time the echo, and multiply by the speed of light to get the range.
A wall of towers
From that experiment grew Chain Home: a ring of coastal stations, each with transmitter towers standing around 360 feet high, sweeping the approaches to Britain. They could pick up formations gathering more than a hundred miles away. The system had blind spots, especially against low-flying aircraft, so a companion network called Chain Home Low was added to watch beneath the main beams. Crude by later standards, it was good enough, and it was ready just in time.
But raw radar returns are just glowing blips on a screen. The true stroke of genius was what Britain did with them.
The Dowding System
Air Chief Marshal Sir Hugh Dowding, head of Fighter Command, wired the whole country together. Radar plots and reports from the ground-based Observer Corps flowed into a Filter Room at Bentley Priory, where they were combined into a single, trusted picture and passed to group and sector stations. There, controllers vectored fighter squadrons straight to the incoming raids. The entire loop, from a blip on a screen to Spitfires climbing to meet the enemy, could take as little as four minutes.
The payoff was enormous. Instead of wearing out its pilots and engines flying wasteful standing patrols, the RAF could keep its fighters on the ground until they were needed, then send them to precisely the right place. A smaller force fought as if it were larger.
The edge that decided the battle
Germany had good radar of its own, but it had nothing like the Dowding System to knit sensors, communications and fighters into one coordinated whole. That integration, not any single gadget, is what let a hard-pressed Supermarine Spitfire force hold off a numerically superior enemy through the summer of 1940. It was the ancestor of every air-defence network flying today, and it was built, just in time, out of towers, telephones and nerve.
Sources: Imperial War Museums, RAF Benevolent Fund, Science Museum, World History Encyclopedia.
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