When a spacecraft performs a splashdown maneuver, a recovery team is standing by to retrieve the capsule and its human contents quickly. A flotation collar is deployed to increase buoyancy and prevent the spacecraft from sinking. If, however, the spacecraft did sink, would it be able to withstand the pressure of the deep?

Structurally speaking, what are the differences between a spaceship floating in the vacuum of space and a submarine floating underwater in an ocean?