[@Skepic] I don't know.  I'm not familiar with them.  But, I've been playing with the idea for years now.  It seems to me that it would require some serious limitations when it comes to hauling and weaponry but it opens alternative doors as well.

For example, attacking a coastal base through its submarine dock and then taking off to distract them while the main force comes in to bomb the distracted AA guns.

Or, firing homing missiles from just under the surface of the water to surprise flying or naval convoys.

Biggest drawback?  Waterlogged machineguns don't work so well.  It couldn't have the nose gun.  Maybe a five charge capacitor with a laser though.  That might work, being a sealed system.