In Germany, the development of the first technologies of sonar and radar were interrelated. Following Christian Hulsmeyer's forgotten invention of the "Telemobiloskop" in 1904, two Berlin engineers, Paul Gunther Erbsloeh and Hans-Karl von Willisen, developed and built devices to locate targets accurately by reflections with underwater sound and radio waves. In 1934, they found their own company for this work, called Gesellschaft fur Elektroakustische und Mechanische Apparate (GEMA), which became the birthplace of their famous Freya air-warning and Seetakt ocean-surveillance radars. Harry...