2010 is not only the seventieth anniversary of the legendary Battle of Britain, it is also the seventieth anniversary of another fi nest hour - that of Radar. The bravery and skill of British pilots in the Second World War, and the fighting capability of their aircraft, would have been in vain had they not been part of a highly complex and sophisticated air defence system based on radar. The development of this system in just five years is one of the most remarkable scientific and technological accomplishments of the twentieth century. Despite this, the creation of radar defence has been somewhat overlooked. Many of the studies on radar have focused on the development of the technology, with little attention given to the creation of the much larger system for integrating it into the nation's air defences. Britain's Shield relates the development of radar with the diplomatic and air policy concerns of the period. It shows how a small group of scientists, engineers, airmen and politicians accomplished this technological miracle, and offers a revisionist appraisal of Churchill's role, showing that his influence was, more often than not, counter-productive to the development of effective air defences