Wow, who took their Wally sub down to 30+ feet?

I don't seal the wiring tubes, so I always find water inside--and I know it seeps next into the radio-receiver "black box" and motors. I've probably lost more than one because, after leakage and some crushage of the buoyancy material, the sub got too heavy and couldn't come back up.

Anyway, that's how plastic RC subs sink. My sub-vet friend told me on manned steel subs you can see the hull caves in between the frame ribs; on new subs it happens until the hull is "set."

I guess it would vary--depending on the design of your sub--where water pressure would start bursting hull fittings or rupture the hull. I would think the implosion is less dramatic than the movies, but indeed air should bubble out of the broken hull in at least one place. With watertight doors shut, then I would think the ruptures might happen compartment-by-compartment, either puncturing the hull in multiple places and/or deforming bulkheads until pressure was equalized throughout.