Belt armor is a layer of heavy metal armor plated onto or within the outer hulls of warships, typically on battleships, battlecruisers and cruisers, and aircraft carriers. Typically, the main armor belt covered the warship from its main deck down to some distance below the waterline. If the armor belt were built within the hull, rather than forming the outer hull, it would be installed at an inclined angle to improve the warship's protection.