The Air Ministry contacted Watson-Watt in January 1935 and asked him to investigate the possibility of damaging enemy aircraft by the use of radio waves. Watson-Watt was quick to show that this was impossible but wrote to the Ministry with another suggestion - "Meanwhile, attention is being turned to the still difficult, but less unpromising problem of radio detection". On February 12th 1935, Watson-Watt drafted a memo entitled 'Detection and Location of Aircraft by Radio Methods'. The proposed technique was simple. It combined results from two on going research topics; the range finding of ionospheric layers and the direction finding techniques previously used to detect thunderstorms.
On February 26th 1935, an experiment was carried out to test the viability of the project. Apparatus from Ditton park was placed near the BBC transmitter at Daventry. The transmitter illuminated an aircraft flying past on a pre-arranged course. At 09.45 the receiver detected the aircraft at an estimated range of eight miles. A. F. Wilkins, a colleague of Watson Watts who had helped in the initial calculations, later said "It was clear to all who watched the tube on that occasion that we were at the beginning of great developments in the art of air defence". The original apparatus used in this historic experiment are now housed at the London Science Museum.