Oceanography

In the First World War, submarines were used. To detect submarines, sonar was invented. Sonar machines broadcast sound pulses into the water, which reflect off submarines. Sonar could both locate and tell how far away submarines were. After the war, sonar was adapted to measure water depth. In the 1920's, this revolutionized scientists’ understanding of the sea floor. As more sonar work was done, underwater volcanoes, mountain ranges, and deep trenches were discovered. Sonar advances continued during and after the Second World War. Sonar work led to the development of the first global map of the sea floor, which was published in the 1960s. This information was very important in developing the geologic theory of plate tectonics.

Principle of sonar