Hey Seahawk,
Yep, has a submarine, a small, odd little thing with bars and lights. No VC, no panel, just pilot it around. Its very basic.
I 'think' they redid some of the controls (keyboard, etc) for it to make it a bit more realistic. At first it was just 'dive to the bottom or rise. It wouldnt coast along at a certain depth, or at least I could never figure out how it was done.
Several of us (devs) wanted to make submarines for it. Some have. They made versions with odd linkages and things to get it to float similar to flying slow underwater (joystick controls). I tried a version that didnt work. But I saw that on the keyboard commands that came out, (if I remember correctly) that they have controls for things now, like ballast, etc. Some big firms that make USA defense things wanted the Submarine thing badly for simulations.
There are only a couple of locations on the sea floor that are modelled. Its called Bathemetry in the Scenery settings window. Clicking it 'on' will make it possible to go underwater. Very merky, low viz, no fish or rocks or sea weed, just rockey looking sea floor. There are one or two adventures for it where one you find a sunken ship and explore it.
Thats about it. It think they have screen shots of it at Prepar3D.com in the Screenshots pages. Its just like that.
For the Developer '30 day only' one-time-payment (not the rotating payment version) you can see what P3D is like. Gives you that underwater sim for 30 days to check out. 9 Gigs to download.
Bill