How does a submarine change its depth in the water?

A submarine changes its depth by adjusting its buoyancy through the use of ballast tanks. When it wants to dive, it takes in water into these tanks, increasing its weight and causing it to sink. To ascend, the submarine expels water from the ballast tanks, typically by using compressed air, which reduces its weight and allows it to rise. This ability to control buoyancy enables submarines to maneuver effectively underwater.