There's obvious differences between the Oceangate sub and this (1 atm difference, this is a thinner steel(?) railroad tanker not a sub), but I think it effectively demonstrates how violent and quick an implosion would be:
Video contents: An experiment where the vacuum safety valves were removed from an oil tanker railroad car, and a vacuum was placed inside the car, resulting in it crumpling in an implosion. There is no gore or other specific disturbing content
https://www.youtube.com/watch?v=Zz95_VvTxZM
Video contents: An experiment where the vacuum safety valves were removed from an oil tanker railroad car, and a vacuum was placed inside the car, resulting in it crumpling in an implosion. There is no gore or other specific disturbing content