Context: Submarines control their depth by adjusting buoyancy.

Application: Submarines feature ballast tanks that can be filled with water or compressed air. To dive, the submarine vents air from the tanks, allowing water to flood in. This increases the vessel's overall weight without changing its volume, resulting in negative buoyancy. To surface, compressed air is blown into the tanks, forcing the water out and restoring positive buoyancy. Achieving neutral buoyancy allows the submarine to hover at a specific depth.

Context: Floating drydocks are essential for repairing and maintaining ships.

Application: A floating drydock must maintain stability while changing its draft significantly. When submerged, its waterplane area is reduced to just the cross-section of its vertical wing walls, drastically lowering its metacenter ($M$). The design must ensure that the center of gravity ($G$) remains below $M$ during all stages of operation, including lifting a heavy ship. Water is carefully pumped out of internal compartments to raise the dock and the ship, requiring precise control to prevent listing or capsize.