Ballast Tank

A ballast tank is a compartment within a ship or submarine that holds water to provide stability, control buoyancy, adjust trim and manage the vessel's load distribution, allowing crews to adjust weight more easily than with traditional stone or iron ballast and to reduce draft when entering shallow water by pumping ballast out. David Bushnell's Turtle, built in 1776 and generally regarded as the first combat submarine, carried the first recorded submarine ballast tank, using it to submerge and resurface. Abraham Lincoln, while practicing law in 1849, patented a ballast-tank system meant to help cargo vessels navigate shallow waterways by adjusting their buoyancy, one of several early adaptations of the same basic idea, itself inspired by the natural buoyancy control of creatures such as blowfish and argonaut octopuses, to different marine engineering problems.