In 1904, German inventor Christian Hülsmeyer built a simple ship detection device for preventing collisions at sea. Leading up to and during WW2, many of the countries around the world developed and refined various radar systems. In addition to showing the angular location of targets, they were also able to determine the range of the target from the antenna. The work of Robert Watson Watt in the UK around 1935 led to the creation of the Chain Home system that was instrumental in detecting incoming German aircraft. Also around that time, aircraft-mounted magnetrons began to be used used to detect submarines.
Radar has been mainly used for military applications, e.g. the tracking of targets and remote surveillance; the Iron Dome in Israel, for instance, is a mobile all-weather air-defence anti-missile system. Since World War 2, though, radar has been used increasingly in many other fields too, such as in telecommunications, in airborne and satellite-based systems for remote sensing and imaging of the surface of the earth, in the medical field, and in monitoring and predicting weather patterns.
Prof Inggs also mentioned the pioneering work by Basil Schonland in South Africa, and that last year was the 75th anniversary of radar in the country. To find out more about that, have a look at this post.