Baffles ( submarine ) The baffles is the area in the water directly behind a submarine or ship through which a hull - mounted sonar cannot hear . This blind spot is caused by the need to insulate the sonar array , commonly mounted near the bow , from the noise of the vessel ' s machinery . Following a vessel by hiding in its baffles was a common submarine surveillance technique during the Cold War , which led to the tactic of " clearing the baffles " to detect followers . Other maneuvers relating to a submarine ' s baffles include the " Crazy Ivan " , a hard turn to both clear the baffles and position the submarine to attack any followers , and " Angles and Dangles " , a five - hour process of rapid direction and speed changes to ensure a submarine was not emitting any noise . The calculated baffles - clearing maneuvers undertaken by Soviet Yankee class ballistic missile submarines were dubbed " Yankee Doodles . " Following a vessel in its baffles is dangerous , because of the high risk of collision . Following the development of the towed - array sonar , which negates the baffles blind spot , such tactics have fallen out of use . Background and etymology . Since a sonar array is extremely sensitive to underwater sounds , it must be protected from the noise generated by machinery on the vessel on which the sonar is installed . Otherwise , its own noise would tend to drown out other sonar targets . To reduce noise , sound - attenuating material is placed between the sonar and the rest of the vessel . This makes the sonar much more effective , but causes a blind spot where this material is : as most hull - mounted sonars are located at the front of the vessel , the resulting blind spot is located directly behind the vessel . 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 . " Maneuvers related to the baffles . Clearing the baffles . 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 . When a submarine clears its baffles , a pursuing submarine must take measures to avoid detection , or worse , collision , with the submarine ahead . In some cases , submarine commanders could choose to clear the baffles by executing one or a series of hard turns in order to not only clear the baffles , but also be in a favorable position to attack the potentially following submarine . Such extreme maneuvers were more commonly used by Soviet Navy submarines during the Cold War than by other forces , leading to the maneuver ' s nickname : " Crazy Ivan " . The " crazy " came from the danger such a maneuver posed to both submarines , first being detection of the following submarine , which was commonly avoided by stopping the engines and going to maximum silence , and secondly by collision , as the momentum of the pursuing boat could result in collision with the leading submarine ; dead ahead in the process of turning sharply . Angles and Dangles . Although not specifically a baffle - clearing maneuver , the exercise known as " Angles and Dangles " ( a series of random figure eights , sharp turns , and random depth changes ) is intended to eliminate the unintended self - noise which could occur during a baffle - clearing event . The exercise is executed at the start of a voyage , in order to determine if loose items aboard the submarine are properly rigged for sea ; loose items can fall or shift position during the sudden maneuvers required during baffle clearing , making noise that could be detected by the opposing submarine . Use of towed array sonars . Most present - day submarines and ships carry a towed array sonar : a sonar sensor mounted on a long cable let out behind the vessel . This can pick up sounds in the area behind the baffles , reducing the need for baffle - clearing maneuvers . One reason for this is that towed - array sonars typically have a different frequency response than hull - mounted sonar sensors . Towed array sensors have conical - shaped beams and as a result , have extremely poor directivity in the " end - fire " regions of the array .