The weakest point(s) would have imploded first immediately crushing those inside, then equalizing the pressure differential and the sub’s rear cone fell to the seafloor.
Mercifully, death would have been within a millisecond for the passengers..................
The photo shows that the bubble-like transparent window in the bow of the submersible is missing. I suspect that a structural failure began in the seam of the bubble, possibly causing a crack in the window that resulted in a catastrophic implosion within a few milliseconds.
12,500 ft/ 33 = 378.79 atmospheres, almost four times the surface pressure of Venus.
Mercifully, death would have been within a millisecond for the passengers.
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I agree, they didn’t feel a thing.