I think, but based on nothing but news stories about this incident, that's common for very deep sea submersibles. It makes sense, the could opt out of a whole b

I think, but based on nothing but news stories about this incident, that's common for very deep sea submersibles. It makes sense, the could opt out of a whole bunch of surface ship concerns and they expect to be launched and retrieved. It also helps simplify the design if you don't have to worry about opening hatches from the inside. That adds complexity and can introduce new failure modes.