The operational use of the UK’s Chain Home radar system in the Battle of Britain was the first time in which radar made a significant contribution to the outcome of military operations. Within 5 years, radar technology had advanced to the point where a wide range of platforms were using radar to detect and intercept other platforms, transforming the way in which air operations were performed. At the same time, a new of activity was developed to prevent the enemy from gaining the benefits of using their radars – this was the start of Electronic Warfare in the radar frequency bands. In the Cold War period that lasted for the next 45 years, the capabilities of radar were further developed to allow control of guided weapons and to assist in the navigation and flight of manned platforms. This in turn presented new challenges for the Electronic Warfare countermeasures. Many of the recent radar and EW products would be recognisable to the pioneers in the fields, but some of the processing and technologies employed to enable the performance would not have been imaginable at the point in the 1930s when they developed Chain Home. The story of radar and electronic warfare will be illustrated by descriptions and operational stories of the equipment developed in the UK by such famous companies as Ferranti and Marconi. The heritage of these companies lives in Selex ES, which are now the UK’s leading supplier of airborne radar and EW.