I found this plaque on a house round the corner from where we were staying in Dusseldorf. "Der Ur-Radar Erfinder" would be the original discoverer of radar. I'd never heard of Christian Hulsmeyer. You can read it for yourself but he was first to patent the idea of using Hertz's discovery that radio waves reflect from metal objects. It was to be applied to shipping to stop collisions. Sadly it never quite worked out.
https://en.wikipedia.org/wiki/Christian_H%C3%BClsmeyer
