The Daventry Experiment: Radar

Our information board describing the Daventry Experiment written by Curator Rod Viveash is one of the most popular exhibit in the museum’s permanent collection. No matter what the exhibition, we have to display this board somewhere because we are always asked about the information it describes.

On the 26th of February 1935, in a field near Weedon an experiment was carried out to test the feasibility of “The Detection and Location of Aircraft by Radio Methods” or what we now call Radar.

Germany was known to be building bomber and fighter aircraft at an alarming rate and it seemed inevitable that an attack by air would soon ensue and a means was sought to detect the invaders in time to scramble our fighter aircraft to intercept them.

Sir Robert Alexander Watson-Watt, Scottish engineer, 1935.

Ideas such as using a high power radio beam to fry the enemy pilots in their planes were soon discounted as a powerful enough transmitter to do this was not feasible. Robert Watson-Watt a research scientist at the National Physical Laboratory had the idea of reflecting a radio wave from the aircraft to detect its presence, he had observed that nearby aircraft caused interference to radio communication. Watson- Watt’s associate Arnold Wilkins calculated that this was possible and to prove the theory they set up the “Daventry Experiment”.

The plan was to set up a sensitive receiver in a van at the field near Weedon, and to fly a Heyford Bomber aircraft along the radio beam from a transmitter at the nearby BBC short wave station at Daventry and detect the reflected beam from the aircraft. The idea was to compare the direct signal from Daventry with the reflected signal from the plane, the path length from Daventry was constant whereas that from the plane varied as it moved up and down the beam. This varying phase shift between the two signals was displayed on the screen of a newly invented device, the oscilloscope.

On the day, Watson- Watt, Arnold Wilkins, and a ministry observer A.P. Rowe watched the dot on the screen rise and fall as the Heyford flew along the Daventry short wave beam, its rate diminishing as it got closer and increasing as the plane got further away from them. The experiment was a resounding success and Watson-Watt and his team went on to develop the “Chain Home” Radar stations round the south east coasts in time for the start of the war in 1939.

History was made in that field that day, it helped protect us from invasion from the sea and air and has developed into the world wide use of Radar that we know today.