Speaking from experience, a large flat deck is a very bad thing to have when in shallow water. Numerous times we've been sucked up to the surface while at a shallow depth. What happens is when near the surface the wave action across that flat deck creates a suction and so pulls the submarine upwards, the larger the flat area the larger the suction force. Just a bit of submarine knowledge I'd thought to share, not trying to stifle your imagination or anything.
