How do submarines dive and surfaces?

According to the Archimedes principle, a solid body, which is released to any fluid such as water and air, is applied by the fluid in the opposite direction of the body's weight, that is, an upward force. This force applied to solid bodies released into the water is called the buoyancy of the water. If the density of the solid body released into the water is lower than the density of the water thanks to the buoyancy of the water, the body will float on the water. This force is the reason why giant ships, which have tons of weight, float on the water.

There are special tanks in the submarines that provide density adjustment. These tanks are called “bile tanks”. Thanks to the bile tanks, submarines can easily dive into the water or float to the surface of the water. The bile tanks are filled with air or water depending on the submarine's staying or diving. For example, when a submarine is on the surface of the water, the bile tanks are filled with air, and the submarine does not go under water as the density of the submarine is less than the density of the surrounding water. When the submarine wants to dive into the water, the upper and lower lids of the bile tanks open. While water enters the bottom covers of the tanks, air comes out from the top covers. Tanks increasingly filled with water increase the weight of the submarine and allow it to dive deeper into the water. When the submarine wants to surface again, air is transferred from the tanks with compressed air to the bile tanks. Compressed air allows the water to come out and the submarine to rise towards the surface of the water.