How do sonar systems detect submarines underwater?

Sonar systems detect submarines underwater by utilizing acoustic waves, as sound travels efficiently through water. These systems generally fall into two categories:123

• Active Sonar: An acoustic projector emits sound waves that travel through the water and reflect off the submarine's hull. A receiver then detects these returning echoes to determine the target's range, bearing, and movement.12
• Passive Sonar: This method involves using sensitive hydrophones to listen for and analyze noise generated by the submarine, such as propeller sounds or machinery vibrations.142

These sensors can be deployed in various ways, including being hull-mounted on surface ships or other submarines, suspended from helicopters as "dunked" sensors, or dropped into the ocean via sonobuoys. Additionally, large arrays of sensors may be placed on the seabed for continuous surveillance.152

Detection is influenced by the physical properties of seawater, such as temperature, salinity, and pressure, which affect the speed of sound and can cause sound waves to refract, potentially creating "shadow zones" where submarines may remain hidden.3