Today marks the 80th anniversary of the first use of radar to detect an aircraft, an event which has particular significance in north Northumberland.
Work that started in a muddy field on a cold February day eight decades ago is continued today in the role played by RAF Boulmer.
That radar system built in the late 1930s has constantly evolved over the years as technology has made huge advances.
Today, the RAF maintains radar coverage of the UK through its Air Surveillance and Control System (ASACS) Force and military and civilian radars including the Lockheed Martin TPS77 radar at Remote Radar Head Brizlee Wood, just outside Alnwick.
Proud of its heritage, the ASACS Force still stands guard over the skies of the United Kingdom, 24 hours a day, seven days a week and 365 days a year, ready to react to any unknown aircraft approaching our shores.
It was at the centre of a drama in the skies above the English Channel last month as Typhoon fighters were scrambled to intercept two Russian bombers.
And last week, British fighter jets were almost certainly scrambled by RAF Boulmer to intercept Russian bombers off the coast of Cornwall.
Without the key contribution of radio direction finding (RDF), which later became known as radar (radio detection and ranging), there might have been a very different outcome to the Second World War.
In 1935, the UK was recovering from the Great Depression of the early 1930s, but government spending was still tightly controlled. War was coming and, as aircraft technology improved and the Germans swiftly increased the size of their air force, the UK appeared to be vulnerable to air attack.
The equation facing the Royal Air Force was relatively simple: Bomber speed was expected to double by the time war broke out, but the distance of targets in Britain from the coast remained the same, which meant that the RAF, without the strength to mount standing patrols over the entire country, needed twice as much warning of the arrival of enemy aircraft in order to defend against them.
Some new technology was needed to give the RAF the edge in order to prevail in the coming air battle.
The Air Ministry set up a committee, chaired by Sir Henry Tizard, to examine scientific advances to help air defence. One line of inquiry was to use radio waves to make a ‘death ray’ to attack enemy aircrew or equipment.
Robert Watson-Watt, head of the government’s Radio Research Laboratory, was asked what he thought of the possibility of such a weapon. Applying what was known about radio waves and heat transfer, he and his primary assistant Arnold Wilkins, wrote a note stating that, with current technology, a ‘death ray’ was impossible. However, they said, radio waves could probably be used to detect aircraft. This seemed to be the edge that the committee was seeking, but first the RAF wanted to see a practical demonstration.
The demonstration was a typically British affair. Lacking their own radio transmitter, Watson-Watt and Wilkins decided to use the BBC’s radio transmitter at Daventry, Northamptonshire.
Wilkins arrived with a Morris van in a field near Litchborough, about five miles away from Daventry, on the evening of February 25, 1935. He needed to set up some equipment for the following day, but the lights inside the van failed, forcing him to fumble around in the dark as he tried to connect delicate electrical equipment.
When he finally finished a few hours later, he found that the Morris had sunk into the mud in the field, which had frozen solid and the van was stuck.
Watson-Watt arrived the following morning with the Secretary of the Air Ministry Committee, Albert Rowe.
A RAF Heyford bomber had been tasked to fly over the demonstration for 20 miles, and to repeat this course between 9.45am and 10.30am. Such was the secrecy that even the RAF crew were not told the reason for their flight.
On the first pass, nothing was seen by the three men crouched in the back of the van, but on the second and third passes signals improved so that on the fourth and final pass the aircraft was tracked for more than four minutes, or about eight miles, using just the radio energy from the Daventry Transmitter reflected by the aircraft.
It was an astounding achievement, given that the idea had only been worked on for a month and the equipment had been cobbled together.
After the success of the demonstration, events moved quickly. A research station was set up. In June, aircraft were being tracked by RDF at 15 miles, by July it was 35 miles and by September 55 miles was possible.
In 1936, the first five of the Chain Home radar stations were opened to detect and track aircraft. By September 3, 1939, the outbreak of war, there were a total of 20 stations providing surveillance over the approaches to the UK from Europe.
From a standing start in February 1935, the RAF and its civilian scientists had provided a radar detection organisation, the Dowding System, that swung the balance of power in the direction of defence.
Later this year the RAF will celebrate the 75th anniversary of the Battle of Britain when the RAF fought desperately in the skies over the United Kingdom to defeat the German Luftwaffe in the summer of 1940.
A large part of that victory was due to the new invention which provided vital early warning of German air raids to the RAF air battle managers, then known as Fighter Controllers, who were able to scramble the Spitfires and Hurricanes of RAF Fighter Command.