The Harwich Radio Direction Finding (RDF) Tower was built just before April 1941 and housed one of the earliest applications of RDF. Ten similar sites were built around the UK covering important rivers, docks and harbours. RDF became better known as RADAR around 1943, an American term short for Radio Detecting And Ranging.
“My God, if I’d known what they were going to do with it, I’d have never have invented it!”
– Sir Robert Watson-Watt, inventor of radar, upon being pulled over for speeding by a policeman using a radar gun in 1956