stan wrote:

It was identifying the reflection of radio signals from a flying
aircraft that led to the development and use of radar.
Radar was major factor in the successful defence of Britain (Britain
1940) against German bombing (The Blitz) early in WWII (1939-1945).
Although it was initially very crude, (It was called Radio-location or
RDF, Radio Direction Finding) at the time.
Unfortunately the first war time US use of radar was misinterpreted
when the Japanese attacked Pearl Harbour in Dec 1941!

Actually it was blocking of a radio transmission by ships passing on a
river that led to the development of radar.

tom
K0TAR