I am with Sprouto on this.
Rezy-Noob mentioned that "units don't take damage if they are deep underwater, aka seton's depth".
That is not actually correct.
I did a simulation on FAF with Cybran's and yes battleship can't hit harm's from mid depth and below. Only close to shore.
However T2 static arty, T3 boomer can do it at any depth.
But static T2 tactical missile launcher can't do any damage at any depth.
With sub's it is the same story.
Simulation done on Seton's map.

Still this should be added automatically to the FAF client in some way.
Or can you make it as a pop-up window that would be present during the loby waiting time. Maybe that would be easier to implement? Same pop-up as you get when the lobby is full, just always on or let's say 10sec after loby is full and when the host makes a switch then that it would pop-up again with refreshed stats??
And the Supreme Score Board mod should be added to the client automatically too - way better then the original!!

I think we should look for a compromise.
As you know the water depth is not the same on the maps. So maybe se should use the depth as a reference point. If it is close to shore of in shallow area the underwater object should be killable by let's say the battleship. But if it's under a deep water there is no logic...