A couple more notes:
-Ships move at well above actual scale speed. (It is more like DSS or Dynamic Simultude Speed)
-Dive planes should be of use to level sub.
-It will be armed with a single BB cannon. So I will have to surface to a "vulnerable depth" to fire my gun. Attacking ships can penetrate a couple inches of water and inflict damage at close ranges with their guns.
-My cannon will shoot one spurt of 15 BBs using a small precharged to 140psi accumulator and a QEV (Quick Exhaust Valve). I thought of using a small co2 cartridge but it takes up too much weight and will affect my ballast due to the change of states (liquid to gas).
-A WTC is of no use to me. I individually waterproof electronic components with conformal coatings (3M Skotchkote). There should be little to "fix". I even pot my servos in epoxy/ coat the boards. I imagine my generic mabuchi 280 size motors will fail periodically (once a year or so). A little preventative maintenance goes a long way. On a larger model I would be inclined to do a WTC for sure.
-I have been sinking models for 8years
The only thing to do after being sunk is dump the water out,patch the holes in the vulnerable skin, and reload/recharge the gun... As long as you have built it properly.
-A single properly placed ballast system seems like a better idea.The goal is a "pitch stable" vessel that can surface and dive multiple times. It seems like intoducing a small quantity of water into a well placed bladder via a peristaltic pump could serve my purposes. It could pump in and out with no check valves. A smaller but higher capacity gear pump with check valves could also be effective. I don't want to use centrifugal... I hate priming issues. I will have no air volume to draw from so it seems like an RCABS type system is not good for me.