Arnold Wilkins' (Watson-Watt's assistant) sketch of the Daventry experiment

Today in 1935, Scottish physicist Robert Watson-Watt demonstrated in Daventry, England, that radio waves could be reflected by an aircraft. The experiment, prompted by fears of the development of death rays by Germany, launched a research program into what later will be called by the US Navy radar, for RAdio Detection And Ranging.

According to Robert Buderi, in The Invention that Changed the World, Watson-Watt said in reaction to the success of the demonstration, “Britain has become an island once more.” 

Buderi puts the event in its historical context: “In the often-mystical process of discovery, a few innovations arise solely from original thinking, flying in the face of convention and challenging the status quo…. Many inventions stem from a hybrid case, whereby the originator brings a unique point of view and set of experiences to known facts. Still other advances can be traced ultimately to the steady march of technology; given the state of the art, they must occur, and often take root in several places at once. So it was for radar–a classic case of simultaneous invention. Within a few months of the Daventry experiment, researchers in at least six other nations were pursuing systems with pulse transmission, cathode ray displays, and distance, elevation, and direction finding.”