What happens when a submarine gets into trouble under the sea?
Forces News has gained exclusive access to Exercise Northern Sun 17, one of the biggest tests the NATO Submarine Rescue System has ever faced.
Britain, Norway and France are partners in the NSRS, which has just been exercised for the first time in the Arctic Circle.
As submarine rescue has developed significantly in the last years, the NSRS can now get to a vehicle anywhere in the world in 72 hours.
Submariners can escape in special immersion suits up to 180 metres, but they won't survive deeper than that.
Their only chance is NEMO, the submarine rescue vehicle.
NEMO mates onto the hatch of the submarine, drains the water, and allows the submariners to escape into its pressurised rescue chamber.
Exercise Northern Sun is about providing reassurance for the submarine service that in any condition, the kit will be working.
Lieutenant Commander Ole Steinsland, CO, HNoMS Utsira, said:
"The system gives us confidence that we can be looked after. Of course, basic submarining is always about not getting into these kind of situations."
As this exercise doesn't take place often, it is a rare opportunity for submariners to become fully qualified as rescue chamber operators.
More: How To Save A Submariner