What is a ballast tank used for?

• A. To adjust buoyancy and trim by taking in or releasing water.
• B. To store crew supplies.
• C. To power the ship.
• D. To house weapon magazines.

Answer: (A)

Ballast tanks are used to control the ship’s buoyancy and trim by taking in or releasing water. By filling ballast tanks, a vessel increases its weight, which lowers buoyancy and helps it sit deeper in the water or dive for submarines; by emptying ballast tanks, weight is reduced, increasing buoyancy and enabling lifting or leveling the vessel to achieve the desired trim. This capability is essential for stability during loading, unloading, and maneuvering, as well as for submarines to dive and surface.

Options about storing crew supplies, powering the ship, or housing weapon magazines don’t fit the function of ballast tanks, which are specifically about managing buoyancy and stability through water ballast.