" Attempts were made in 1941 to design a similar proximity fuze, using a tiny Radar set arranged to explode the warhead when the projectile passed near the aircraft. Successful preliminary experiments were made, but before this fuze was developed in England the Americans, to whom we imparted our knowledge, actually succeeded not only in perfecting the instrument but in reducing its size so much that the whole thing could be put into the head not merely of a rocket but of a shell. These so-called “Proximity Fuzes”, made in the United States, were used in great numbers in the last year of the war, "

― Winston S. Churchill , Their Finest Hour (The Second World War, #2)