How do helicopters use dunked sonar to search for submarines?

Naval helicopters utilize "dunked" or "dipping" sonar to detect and locate submarines by lowering a sensor into the water via a cable.12

This process functions through the following mechanisms:

• Deployment: The helicopter hovers over a specific area and lowers the sonar transducer—housed in an oil-filled unit—into the water.13
• Acoustic Detection: The system operates using either active or passive sonar. In active mode, the transducer emits sound waves that reflect off a target, allowing the crew to determine the submarine's range, bearing, and motion. In passive mode, the sensor listens for the acoustic signatures produced by the submarine.31
• Tactical Integration: Once a target is identified, these helicopters can coordinate with mother ships or other assets to track the vessel and, if necessary, launch self-homing torpedoes to neutralize the threat.2

This mobile capability allows helicopters to fill coverage gaps left by stationary sensors or ship-mounted systems, providing a flexible and rapid response to underwater threats.1