In the 1920s and 1930s, the scientific understanding of the behavior of sound in the ocean and its function towards sonar systems for anti-submarine warfare progressed slowly. It was only after an increase in submarine threat at the beginning of World War II in 1939 that a major national effort started to study underwater acoustics.
As a result of the increase interest, a series of results emerged that showed the transmission of sound in the sea, particularly how effectively it could be used to detect submarines, depended crucially on how the temperature and salinity (how salty the water is) of the water varied with depth. Soon, scientists discovered that sound rays bend underwater in ways that are closely linked to the variation of the speed of sound from place to place, and that this could create "shadow zones" in which an enemy could hide.
Discoveries such as these widened the range of oceanic phenomena of interest to oceanographers. Also, with concerns of water depth, winds, and currents, the need to measure and understand underwater physical parameters like water temperature, salinity, and the sound speed at increasing depths was a major priority. Because of this, new kinds of instruments, analysis techniques, new ways of interpreting data, and a broadening of the scientific disciplines were needed in oceanography for military applications.
- Victoria Mehlhaff -
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