I have suggested forking current ships into different categories or types
before, but I will not dwell into that now.

As far as I can see, ships are an attempt to find a fine balance between
exciting PvP (which are thin in present BatMUD, thank Aveallis) and more
traditional PvE aspects.

Please, give us pansyass casual enthusiasts a peaceful means of
intercontinental travel - give us submarines!

Submarines would not be out of medieval fantasy genre at all - at the moment
they are commonplace gnomistry and a result of science, advanced piping,
dukonium pressure hull engineering and experimental steam power. With this
rate of research and development funding they are just about to be mainstream
anyway.

I my opinion, submergicibles would be max class 3 ships with no extra modules
and they would be pretty slow (especially while diving). They would not be
able to engage in a naval battle of any kind (against player or NPC ships).
While diving they could not be seen on the map and with normal view command
they would only see depths of the sea (through the periscope, of course!).

And no, they would not be able to fly over land.