The planet is mostly water so a submersible craft is your only means to explore it.
Our submersible craft entered the undersea shelter through a huge flood-chamber.
Why, a suitable ship to handle a deep submersible craft, let alone the submersible itself, may cost up to $5,000 a day.
Nuclear power revolutionized the submarine, finally making it a true "underwater" vessel, rather than a "submersible" craft, which could only stay underwater for limited periods.
It is also possible to travel under the surface of the water in a submersible craft.
A moon pool also allows divers or small submersible craft to enter or leave the water easily and in a more protected environment.
It was a double-hulled fully submersible craft with both compressed air and ballast tanks between the hulls.
The Skylark fell in behind the submersible craft, close enough to keep it plainly visible.
Station IX developed several miniature submersible craft.
Photographs of the ocean bottom can be taken with cameras that are installed in submersible craft or suspended by cable from surface vessels.