Abstract: When a submarine changes its depth, target tracking of its sonar may become unstable due to deterioration of the received signal,to,noise ratio. In this paper, factors affecting the tracking are studied based on the sonar equation and an analysis of the sound transmission loss. The condition under which sonar can keep tracking with change in depth of the host submarine is presented. It is shown that tracking can be preserved by changing the submarine's speed accordingly so that its self,noise is adjusted to satisfy the condition for target detection.