The U.S. Navy is equipping its anti-submarine helicopters with a new AN/AQS-22 Airborne Low-Frequency Sonar (ALFS). This model operates at higher and lower frequencies than existing sonars, providing the ability to cover four times as much area. The AN/AQS-22 operates in active (broadcasting) and passive (just listening) mode. This is a dipping sonar, which is lowered into the water from the helicopter using a 806 meter (2,500 foot) cable and winch. Overall, the AN/AQS-22 is a big improvement for navy helicopter anti-submarine capabilities.
The U.S. Navy's MH-60R anti-submarine helicopter is a navalized version of the army UH-60. The crew spends a lot of time just operating their computers, sonar and radar in their search for submarines. This work involves staring at a screen most of the time, while manipulating the sensors and computers to detect and locate subs. Once you have a solid location fix, you can launch a torpedo and sink the enemy vessel.
The MH-60R is also equipped with a radar system for detecting subs on the surface, or just beneath the surface (with only the periscope or schnorkel, which provides air for the diesel engine, and gets rid of the exhaust fumes). The sonar system consists of a dipping sonar (connected to the helicopter via a cable) and sonobuoys, that are dropped and communicate wirelessly.