Each submarines have ballasts tank in them. As you may ask what is a ballast tank,a ballast tank is a tank that allows the submarine to float or sink. Each ballast tank contains both air and water.
To sink, air is let out of the tank and water is let in.
To float back up, more air is pumped into the tank,causing it to be lighter,less dense.
As water is let in, it becomes heavier and thus, it becomes denser and would sink.This is a picture of a ballast tank used in a submarine.
In order for the submarine to maintain constant depth throughtout the whole journey, the ballast tank must have the same certain amount of water and air. This is called NEUTRAL BUOYANCY.
This is a whole diagram of a submarine. There are two ballast tanks. One of it is the main ballast tank while the other is the aft ballast.
AN ACCIDENT THAT RESULTED DEATH:
--An accident occured 9 years ago (2000). A Russian submarine K-141 had sunk while preparindg to fire dummy torpedoes.
It is believed that a chemical ,used as a propellant for the torpedo, seeped through rust in the torpedo casing.
Another belief is that a chemical cartridge came in contact with water that had cause chemical reaction and flash fire.
Fortunately, 23 out of 118 sailors had survived the attack and even stayed at compartment 9 at the aft of the boat for a few hours after the blast.
There were arguments about survivers still living after the blast but was later confirmed with evidence from Captain Lieutenant Dmitry Kolesnikov, one of the remaining survivers. He had written notes about his stay. The unfortunate event was that they had died hours later.
Tragedy broke out on the Summer of August 12, 2000. The ship could resist no more and SUNK! The news had spread throughout the world and it has devastated everyone-nobody expected it to happen. Shortly after two years later (2002), it was confirmed that a faulty torpedo had sunk KURSK.