How can a submarine be identified by its sound signature?

Submarines are identified by their sound signatures primarily through the use of passive sonar, a technique that detects and analyzes the noise naturally emanating from a vessel. Unlike active sonar, which relies on bouncing sound waves off a hull, passive systems utilize sensitive receivers to intercept specific acoustic patterns produced by the submarine.123

These sound signatures are generated by various internal and external sources, including:

• Machinery Noise: Pumps, particularly those used to circulate reactor coolant in nuclear submarines, create distinct acoustic signatures.2
• Propulsion Noise: The rotation of propellers and other mechanical movement generates noise that can be intercepted by sonar arrays.43

Because these sounds are unique to the vessel's design and mechanical state, they serve as identifying characteristics. To counter this, modern submarine design prioritizes "silencing," which involves mounting machinery on sound-absorbing materials and coating hulls with sound-absorbent substances to minimize the acoustic footprint. These signals are captured by sensors on surface ships, other submarines, or stationary arrays on the seabed, allowing for the detection and tracking of submerged vessels.1243