Since news of the missing sub broke, I’ve been thinking implosion and thinking about an episode of Mythbusters where they attempted to answer the question: Can a deep-sea diver’s body be crushed into his helmet if his air hose breaks?
The idea was that if a deep sea diver’s air hose is cut, the pressure differences between the water and inside of the suit will cause the diver’s body to be crushed and pushed up into his helmet.
The Mythbusters made a meat mannequin, filled with organs, put it into a deep dive pressure suit with an old diving helmet and dropped it 300 feet into the ocean. IIRC, the myth was partially confirmed.
I saw that Mythbusters show, the diving helmut was filled up with “meat” and “organs”. They also did a railroad tank implosion by creating a vacuum in the railroad tank. Less than a second to crush the tank like a squashed beer can.