From the moment it was requisitioned by the government at the beginning of the war, Warnham Court had a secret existence.

In 1941, it became home to the Signals Experimental Establishment, a government agency concerned with the development of radio and radar. The SEE normal peacetime location was at Woolwich Common but it was feared that it was vulnerable to enemy bombing, especially no doubt because of it's closeness to Woolwich Arsenal and the Docks.

It's not known how much research and development of radar was done but certainly there were advances in military radio developed at Warnham.

Because after the British raid on a German radar site at Bruneval on the French Coast, SEE (or Signals Research and Development Establishment as it became known) and it was feared that Warnham was possibly within reach of German raids, it moved to Christchurch in Hampshire.

After that, Warnham became STS 63, a Secret Training School of the Special Operations Executive (SOE) which trained agents to operate in enemy controlled territory. STS 63 was one of a number of establishments for Polish agents and they would come to Warnham for the shooting segment of their training.