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Sonobuoys are canisters ejected from maritime patrol aircraft that detect submarines. A sonobuoy is about the four times the size of a can of Pringles Chips. When it hits the water it floats. The bottom of the canister drops a hydrophone (underwater microphone) to a pre-programmed depth (30, 210 or 300 meters). The sonobuoy then relays the noise picked up by the hydrophone back to the aircraft via radio. Back in the aircraft, a technician interprets the noise and can find range, bearing to, course, speed and type of the submarine.

In the aircraft, the hunt is on. An Anti-Submarine Warfare(ASW) aircraft will typically drop a pattern of six to ten buoys at a time. The giant line of listening sonobuoys will detect the noise of any submarines in the area. Once the ASW aircraft knows the rough location of the sub by using two bearings from sonobuoys to pinpoint the location, the ASW aircraft will make a circle of sonobuoys around the sub to gather more information on course, speed, depth and type of the sub. Once the ASW aircraft has determined that the submarine is hostile, the attack begins. The Aircraft will drop another sonobuoy on top of where it thinks the submarine is. The ASW officer in the aircraft will then turn the sonobuoy active, which means using active sonar, or pinging. This pinging will pinpoint the exact location of the submarine. The only downfall is that active pinging will let the submarine know that he is being hunted. Now the submarine will try to evade. The next step for the ASW aircraft is to line up on an attack run and drop a torpedo onto the submarine. The torpedo will be fed with the latest data on the submarines position until the time of drop. Once dropped, the torpedo will go active, again using active sonar, or pinging, to home in on its target.

There are many variations on the sonobuoy. Along with active and passive modes, there are also special buoys designed to drop a sensor that tells the aircraft of temperature and salinity changes which affect sonar performance. Also, there is a communication buoy which relays communications signals from friendly aircraft to friendly submarines.

To learn more about Anti-Submarine Aircraft, check out these nodes:
Ilyushin Il-38 May
Lockheed P-3 Orion
Lockheed S-3 Viking
British Aerospace Nimrod

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