Throughout WWII it provided the RAF with nearly a half ... measuring the lag of return pings between various stations, the system could identify and track incoming squadrons within five degrees ...

However, he could hear the guns when the German Bombers were still a long way off, whereas we couldn’t. So he would go under the stairs. And this was our early warning system.

Acoustic mirrors were the very first—and very crude—early-warning system, built years before ... 1930s to detect German aircraft. Before World War II had even ended, though, they were obsolete ...

This mad rush became a thing of the past when I discovered that I had my own early warning system, so much more reliable than radar and the siren. I had a bed where the mattress rested on a metal ...