HUET is the acronym for Helicopter Underwater Escape (or Egress) Training which offshore workers have to undergo as part of the requirements for working on offshore platforms and oil rigs.
The "dunker" is the part which most dread - especially for non-swimmers. Personnel not only have to practice escaping from a dummy helicopter lowered in to a tank but also have to escape from the module when it is capsized.
The shots inside were taken by undergoing the process a number of times and very hit or miss and using a torch wrapped in a sandwich bag for lighting.
Some video footage was done using a Hero sports camera and the results were edited to fit with an appropriate piece of music - "Extreme Ways" - the theme music from the Bourne Ultimatum. A bit of self-indulgence.
Video of HUET