[jedc]

former US submariner here:

* forward-facing sonar is always being used at all times while a submarine is underway

* however, the sonar that's always used is passive, and since mountains don't move, passive sonar doesn't find them

* active sonar could theoretically be used, but the risk of communicating a submarine's position relative to the chance that you'd hit an underwater mountain is balanced strongly on the side of running silent.

[contingencies]

Thanks for sharing an informed perspective!