Submarine cables are only suitable for use under water, that is what they are made for.
A submarine is only used under water.
Without breathing, the world record is 22min With air bottles (scuba diver) or in a submarine you can of course stay longer. In a submarine when you have enough supplies, you can stay virtually forever under water.
The submarine is under water.
For modern nuclear subs, they could theoretically stay under indefinitely. Of course, there's a crew which has to eat and bathe, and food and toiletries do eventually run out.
Submarine.
Yes they can!
it is a under water earthquake
In war a submarine can hide under the water and attack without being seen.
A submarine.
A submarine.
no unless you are in a submarine.