What are the water tanks in submarines that provide weight called?

Ballast tanks are specifically designed to hold water and adjust the buoyancy of a submarine, allowing it to dive or surface as needed. When a submarine takes in water into its ballast tanks, it becomes heavier and can sink. Conversely, when it expels that water, it reduces its weight, allowing it to rise to the surface. This fundamental principle of buoyancy is crucial for submarines to operate effectively underwater.

The other terms do not accurately describe the function or purpose of the ballast tanks. Air tanks may refer to compartments for storing air but do not contribute to weight management. Service tanks typically hold other operational fluids necessary for various systems on the submarine, while water tanks might suggest general storage but lack the specific buoyancy control aspect associated with ballast tanks.