Too small. Think bigger! Like, a full size mini sub. You can take pics through the porthole.

So many people out there making such cool stuff. I remember seeing a website where the guy was making a scale WWII german sub. Welded steel, the thing was supposed to be nearly as capable as the real thing - minus the torpedos, of course.
I've also seen sites of mini subs where you wear full scuba gear, but sit in a little bubble.
Anyway, be sure to post pics if you ever do make something!