The
history of radar starts with experiments by
Heinrich Hertz in the late 19th century that showed that radio waves were reflected by metallic objects. This possibility was suggested in
James Clerk Maxwell's seminal work on
electromagnetism. However, it was not until the early 20th century that systems able to use these principles were becoming widely available, and it was German inventor
Christian Hülsmeyer who first used them to build a simple ship detection device intended to help avoid collisions in fog (Reichspatent Nr. 165546). Numerous similar systems, which provided directional information to objects over short ranges, were developed over the next two decades.