Beginning in the early 1950s, the United States and British navies began to investigate the use of passive sonar in which an array of sensors detect noises emanating from the target submarine. Prior to this new method of detection, navies would use active sonar whereby a submarine would emit a signal that would reflect off the target submarine. Unfortunately, this would, in turn, let the target know it was being monitored.
Passive sonar systems allow the submarine to become ‘stealthy’ by ‘listening’ to noise emitted from the target submarine and by utilizing a series of sensors, equally spaced on a cable, to receive the signals from the target passively. Powerful sonar algorithms convert the signals (pressure fields) into information whereby the submarine can take action.
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