The idea of using electromagnetic waves to locate ships was registered as a patent in Germany, England and France as early as 1904 by the Düsseldorf engineer Christian Hülsmeyer.
On April 30, 1904, the Imperial Patent Office patented Christian Hülsmeyer's „method for reporting distant metallic objects to an observer by means of electric waves“ under No. 165 546.
The patent specification contains an illustration of a steamer using back radiation to detect an oncoming ship. Tests carried out on the Rhine had in principle shown the usefulness of the method. In addition to this „telemobiloscope“ (remote motion viewer), Hülsmeyer was granted a patent on November 11, 1904, for determining distance by measuring the angle of elevation.
This marked the birth of the radar method by Christian Hülsmeier:
A successful demonstration on the Rhine proved the technical function of the method. However, due to the inadequacies of high-frequency components at that time, no outstanding ranges were achieved. Therefore, the method met with general disinterest for the time being.