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Anti-submarine warfare is one of the least well-known forms of combat. Submarines rely on the opacity of the world’s oceans to evade detection, sneaking up on enemy ships before ambushing them with a brace of missiles or torpedoes. Modern submarines can attack their targets while fully submerged, making visual or radar detection impossible. Anti-submarine warfare hunters must find them via sound, using sonar to detect lurking submarines.

The US Navy wants to enhance its capabilities in detecting and targeting enemy submarine threats. The service has recently decided to purchase up to 18,000 AN/SSQ-125 sonobuoys from Lockheed Martin and ERAPSCO. Sonobuoys are highly sensitive floating receivers that help pinpoint the locations of submarines.

Instead of using active sonar, submarines can be identified by aircraft that figure out the direction in which the enemy subs are traveling. The floating sonobuoy sensors can listen to the ocean and relay that data to aircraft flying above. 

The long, thin buoy is one portion of the two-part Air Deployable Active Receiver (ADAR) system. An aircraft, helicopter, or even a surface ship will drop AN/SSQ-101 and AN/SSQ-125 sonobuoys in an attempt to find an enemy sub.

Once released, the AN/SSQ-101 enters the water and deploys its payload. It releases a floating transmitter that bobs on the surface of the ocean, relaying whatever information it finds to nearby friendly ships and aircraft. Next, the sonobuoy unfolds a five-sided array of 40 underwater microphones (known as hydrophones), creating an underwater listening post.

The other half of the ADAR system is the AN/SSQ-110A sonobuoy, consisting of two explosive charges. Each time an explosive charge detonates, it sends a pulse of sound energy through the surrounding water. These pulses, especially those bouncing off of enemy submarines, are picked up by the listening AN/SSQ-101. The newer AN/SSQ-125, which replaces explosive charges with electronically generated sound, is replacing the -110A, according to popularmechanics.com.