According to the website of Popular Mechanics on January 6, 2022, the rise of the Chinese navy, coupled with Russia's formation of a fleet consisting of powerful Yasen class and Borealis class nuclear submarines, has led many navies, including the powerful US navy, to prioritize anti submarine warfare (ASW) as a development goal.The article points out that last month, the US Navy decided to purchase up to 18000 AN/SSQ-125 sonar buoys, which are highly sensitive floating receivers that help accurately locate the position of submarines.

Russian "God of the North Wind" class ballistic missile nuclear submarine

The article states that anti submarine warfare is one of the least well-known forms of warfare, which makes naval investment particularly interesting. Submarines rely on the opacity of the world's oceans to evade detection, secretly approach enemy ships, and then ambush them with missiles or torpedoes. Modern submarines can attack targets underwater, rendering visual or radar detection ineffective. Anti submarine hunters must locate them through sound and use sonar to detect lurking submarines. One method is to use what is called 'active sonar'. Active detection is the use of sound explosion energy transmitted through water to detect invisible objects. The movie 'The Hunt for Red October' caused a sensation as soon as it was released in 1990. When a sonic boom propagates in water, it is bounced back by underwater objects, and the crew on the submarine can analyze the sonar echo to determine if it is coming from an enemy submarine. Calculating the time required for sound wave return can also enable submarine hunters to determine the direction of enemy submarines' movement.Another method of identifying submarines is through airplanes, and it is very effective. Anti submarine patrol aircraft can conduct long-range searches and respond quickly to enemy submarine intelligence. However, the problem with airplanes is that unlike surface vessels and other submarines, they cannot use any built-in sonar equipment because they fly on the surface of the water instead of crossing it. At this point, the sonar buoy needs to come into play. These floating sensors can monitor the ocean and transmit data to aircraft flying on it. The slender sonar buoy is part of an active receiver (ADAR) system consisting of two components. P-3 or P-8 anti submarine aircraft, MH-60 "Seahawk" helicopters, and even surface vessels deploy AN/SSQ-101 and AN/SSQ-125 sonar buoys in an attempt to locate enemy submarines. Once released, the AN/SSQ-101 sonar buoy enters the water and deploys its payload. The first thing it releases is a transmitter floating on the sea surface, transmitting any information it discovers to nearby friendly ships and planes. Next, the sonar buoy unfolds a five sided array consisting of 40 underwater microphones (known as hydrophones)Form an underwater monitoring network.

Operation diagram of AN/SSQ-101 and AN/SSQ-125 sonar buoys

The other part of the system is the AN/SSQ-110A sonar buoy. AN/SSQ-110A consists of two explosive sound source loads. Every time an explosive explodes, it emits sound energy pulses through the surrounding water. These pulses, especially those bounced back from enemy submarines, were received by the AN/SSQ-101 monitoring device. Anti submarine fighters typically deploy multiple AN/SSQ-101 sonar buoys, hoping that their data can help locate enemy submarines through triangulation. The newer AN/SSQ-125 sonar buoy replaces explosives with electronically generated sound and is replacing the AN/SSQ-110A sonar buoy.

Source: Military of Strong Countries