History
The first early warning radars were the British Chain Home, the US CXAM (Navy) and SCR-270 (Army), and the German Freya. By modern standards these were quite short range, typically about 100 to 150 miles. This "short" distance is a side effect of radio propagation at the long wavelengths being used at the time, which were generally limited to line-of-sight. Although techniques for long-range propagation were known and widely used for shortwave radio, the ability to process the complex return signal was simply not possible at the time.
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