Reginald Fessenden
Reginald Aubrey Fessenden (October 6, 1866 – July 22, 1932) was a Canadian-born inventor, who did a majority of his work in the United States and also claimed U.S. citizenship through his American-born father. During his life he received hundreds of patents in various fields, most notably ones related to radio and sonar.
Alexander Behm
Alexander Behm (11 November 1880 in Sternberg (Mecklenburg) – 22 January 1952 in Tarp (Schleswig-Flensburg)) was a German physicist who developed working ocean echo sounder in Germany at the same time Reginald Fessenden was doing so in North America.