Who invented the radar in 1904?

This work led to the Airborne Interception Mk. IV , the first production air-to-air radar system. Mk. IV entered service in July 1940 and reached widespread availability on the Bristol Beaufighter by early 1941.

The first practical radar system was produced in 1935 by the British physicist Sir Robert Watson-Watt, and by 1939 England had established a chain of radar stations along its south and east coasts to detect aggressors in the air or on the sea.

It was first used in combat early in 1944 on the Anzio beachhead in Italy. Its introduction was timely, since the Germans by that time had learned how to jam its predecessor, the SCR-268.

Robert Watson-Watt is given the credit for inventing the radar. In fact, this credit should go to the German engineer Christian Hulsmeyer who in 1904, using patented an early warning system for shipping.