Belt armor

Belt armor is armor added to the hulls of battleships. Specifically, it is an additional layer of plating on the outer hull that is held about five feet away from the "actual" hull. The benefits of this addition are twofold. First, they add extra buoyancy by creating a large area of negative space over much of the hull. More importantly, however, belt armor acts much like the reactive armor currently found on many main battle tanks. If breached by ordinance, this armor would be destroyed, but the vessel would still maintain hull integrity. Several wartime vessels are noted for their thin or shallow belt armor due to attempts to rush production and conserve supplies.