Torpedo

A Torpedo system is a standard Long Range Missile or Short Range Missile launcher that has been modified to fire its missiles through water rather than air. They are typically used by submarines and other naval vessels to attack targets that are underwater.

They're identical in every way to their more common cousins, but they must be fired from or into Depth 1 or greater water, and they must stay in Depth 1 or greater water as they make their way to their target.