Oh and by the way, the crew is sealed inside the vessel by bolts applied from the outside.
“There's no way to escape, even if you rise to the surface by yourself. You cannot get out of the sub without a crew on the outside letting you out,” said Pogue, who must be shacking furiously right now. It could have been him right now stuck inside some god-forsaken piece of junk with a gazillion tons of water above his shoulders.