Chain Home and the Battle of Britain
Britain's Chain Home network — 21 transmitting stations along the south and east coasts by July 1940 — gave RAF Fighter Command something no air force had ever had: 20 minutes of warning before a raid arrived. The radar itself was crude. It used 12-metre wavelengths and could not measure altitude reliably. But combined with the Dowding System, which fused radar tracks with observer reports and routed them through a single command, it doubled the effective strength of Fighter Command.
Without Chain Home, the RAF would have had to keep a third of its fighters airborne at all times just to be sure of catching incoming bombers. With it, fighters scrambled only when a raid was confirmed. That single efficiency probably won the Battle of Britain.
Airborne intercept — radar in the cockpit
The cavity magnetron made microwave radar small. By 1942, the British AI Mk. VIII fit inside a Beaufighter's nose. The pilot could chase a Heinkel through cloud at night using a tiny green CRT. By 1944, the US SCR-720 was in P-61 Black Widows over Europe and the Pacific. German night-fighter losses to RAF Bomber Command were largely the work of three things: Window (chaff), Monica (tail-warning radar), and the H2S ground-mapping radar that let bombers find cities through 10/10ths cloud.
The proximity fuze — radar inside a shell
Possibly the most extraordinary radar of the war: a complete pulse-doppler radar squeezed into the nose of an artillery shell, robust enough to survive 20,000 g of acceleration, cheap enough to throw away. The VT (variable time) fuze detected when the shell passed within 20 metres of a target and detonated. It quadrupled the lethality of US anti-aircraft fire and was decisive against V-1 cruise missiles in 1944.
What didn't change
By 1945 every concept in modern radar — pulse, Doppler, PPI display, IFF, monopulse tracking, synthetic aperture, electronic countermeasures — had been invented or proven in combat. The last 80 years have been refinement, miniaturisation and software. The core physics is 1944.