“Won’t he hear us?”

“Not if you in his baffles Seaman Beaumont, Not if your in his baffles.”

The baffles being referred to is the blind spot directly behind a surface ship or submarine while it is underwater. 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.

For a submarine the baffle is a cone that extends directly behind the sub. The cone is an area of dead silence for the sub as it cannot hear. This problem has been solved by use of a towed sonar array. This is another sonar device that trails the sub, normally at a lower depth. This allows the sub to hear all around its self and then stop anyone from following it. Surface ships use a similar piece of equipment to allow them to hear subs and other surface ships.

A submarine tracking another submarine can take advantage of its 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 first off it is not heard by the submarine ahead, and secondly it does not collide with the submarine ahead.