Radar started in the late 19th century. With experiments by Heinrich Herts but it was German inventor Christian hulsmeyer who first used them to build ships detention devise to help avoid collisions in fog.

Who?

In 1936 Paul e Watson helped in the development of a system that on December 14 1936 detected an aircraft flying in and out of New York at ranges of up to 7 miles.  U 1938 this involved into the army's first radio position findings.