Baffles (submarine)
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The baffles is the area in the water directly behind a submarine or ship through which a hull-mounted sonar cannot hear. Since the sonar array is extremely sensitive to underwater sounds, it must be protected from the noise generated by machinery on the vessel using the sonar. Otherwise, its own noise would tend to drown out other sonar targets. To reduce noise, acoustic baffles and sound-attenuating material are placed between the sonar and the rest of the vessel. This makes the sonar much more effective, but causes a blind spot in the direction of the baffles. Since most hull-mounted sonars are located at the front of the vessel, the baffles are behind the sonar and the resulting blind spot is located directly behind the vessel.
A submarine tracking another submarine can take advantage of its quarry’s baffles to follow at a close distance without being detected. Periodically a submarine will perform a maneuver called clearing the baffles, in which the boat will turn left or right far enough to listen with the sonar for a few minutes in the area that was previously blocked by the baffles. Good tactics require a submarine to clear the baffles at irregular intervals and in different directions so that a pursuing submarine cannot predict when and how the next baffle-clearing maneuver will be made. Sonar operators in a pursuing submarine must be very vigilant and inform the conning officer immediately as soon as the quarry begins a turn. At that point the pursuing submarine must take measures to ensure that (1) it is not heard by the submarine ahead, and (2) it does not collide with the submarine ahead.
A sudden, sharp baffle-clearing turn at speed is sometimes called a "Crazy Ivan" by submarine sailors of the U.S. Navy. This maneuver was named for its occasional use by submarines of the Soviet Navy during the Cold War. U.S. Navy submarines commonly shadowed Soviet submarines in their baffles during the Cold War.
Most present-day submarines and ASW ships have a towed array sonar that is towed behind the ship and can pick up sounds in the area behind the baffles.
The term baffles is likely derived from a lesser used definition of the word itself, that of "a partition that prevents interference between sound waves in a loudspeaker." In the instance of its usage in terminology pertaining to submarines the definition can be expanded and slightly modified to 'an area behind the submarine that due to the cavitation and the wake left by the propulsion system impedes the ability for on-board sonar systems to accurately establish what if anything is behind the submarine."
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