I had to do the US Navy Swim Phys (which, amongst other things like the helo dunker) consists of swimming 100m in full flight gear with the lofe preserver deflated (flying suit, flight boots, g-pants, harness, life preserver, helmet, gloves), thread water for 10 minutes and inflate the life preserver orally (ie: no CO2 cartridge).
It was probably the most difficult physical test I have taken and probably the most relevant to what I do.