During WWII, the Germans were using radio beacons (the “Knickebein” system) to guide their bombers into English territory. They set up two beacons, one in Kleve, a city in western Germany, and one at Stollberg Hill (North Frisia). The two radio beams intersected over Derby.
Source:
https://de.wikipedia.org/wiki/Knickebein_(Funkfeuer)
A Flat Earther has claimed that this would be impossible on a globe earth (see here ... Read even more
