In 1914, Marconi engineers based in Chelmsford detected radio signals from German airships. The British Royal Navy recognised the importance of this and set up a chain of Direction-Finding stations on the East Coast of the UK. By 1916, a network had been established that enabled successful defence of the UK from air attacks. In the 2nd World War, the German Air Defence system was very effective, using a mixture of radar, radio and EW systems. The British and American activities to defeat this Air Defence system, and later variants produced by the Warsaw Pact, employed a wide range of equipment that would be familiar to the Electronic Warfare engineers of 2014. This talk commemorates 100 years of British activity in Electronic Warfare in support of Air Operations.