Active sonars are often plagued by false contacts from fish, which are much more numerous than the submarine targets that the sonar is actually trying to find. Even though submarines are much larger and therefore produce much larger echoes than do fish located at similar ranges, fish located near the sonar can produce echoes that confuse the sonar operator. Bayes's theorem provides a convenient framework for defining a range weighting technique to help ignore unwanted sonar contacts from nearby fish.