The Submarine in War and Peace — Simon Lake

" ...]tons hung by an arm twelve inches long, and it would require the same force to incline the ship as it would to incline the pendulum. Therefore it is evident that the greater the metacentric height the more stable the ship, and the less likely she is to make eccentric dives to the bottom or "broach" to the surface. Ballast Tanks.-All submarines are fitted with tanks which may be filled with water so that the vessel will submerge; these are called ballast tanks. When ...]."