Submarines have the capability of taking on, or getting rid of ballast, to make themselves heavier or lighter as the situation requires.
Normal ships are designed to move on the surface of the water. Submarines are designed to be able to submerge and travel under the water's surface, as well as on the surface. When normal ships go down, they stay down. Submarines are able to come back up after they go down. All American submarines are nuclear powered. With the exception of Aircraft carriers, surface ships are powered conventially.
Submarines must be able to float to load and offload crew and cargo and to have repairs and maintenance. They are designed to submerge either for underwater exploration or to pass undetected by ships at the surface and planes and satellites above.
Submarines are designed with enough ballast and control systems to allow them to submerge and surface as needed.Surface ships are designed only with enough ballast and control systems to keep them on the surface. While they can sink just as well as submarines can, their ability to re-surface without a salvage operation is non-existent.
"Subduction" is what the earth does. Submarines "submerge".
By their pumps and ballast-tanks: allowing water into the tanks to raise the vessel's density so can submerge, or pumping air into the tanks to displace the water and allow the submarine to surface.
Dry, surface...
The density will rise and submerge the submarine.
to sink below the surface of water
All submarines can sink. Some can return to the surface.
A ballast tank is one of several external or internal tanks fitted in submarines, which allow the boat to submerge when filled with water.
The root word for submerge is "merge," which means to combine or blend. The prefix "sub-" means under or beneath, so submerge means to put something below the surface of water or liquid.
(Submerge is a verb meaning to put under water or to go below the surface of the water. It can also mean to obscure or subordinate. Also submerse.)Examples:The toddler wanted to submerge all his toys in the bathtub, but his mother took them away.He stood on the dock, watching the pieces of the boat submerge.Her career threatened to submerge her personal life.