In reply to Brendan H:
It involves being dunked into a swimming pool in a plastic fake helicopter simulator, turned upside down and having to make an escape while wearing lifejacket and rebreather type kit.
All under supervision of Divers in the water.
You can do it in a few places, Falck Nutec, HOTA, RGIT Altens, Fleetwood etc.
Refresh every 4 years.
Australia? Scrap all the above, you may have different regs / requirements