This gun had two important innovations. First, it was breech-loading, meaning that the ammunition was loaded directly into the back end of the gun instead of being tamped down into the barrel from the front. The second innovation was the method by which the gun barrel was cooled. Leonardo set this gun barrel inside a copper casing that was filled with water. Once the gun was fired, the barrel would cool off rapidly because the water would absorb the heat. Water-cooled barrels, used extensively during World War I, are important for guns that have a high rate of firing, to keep the buildup of heat from damaging the barrel. (See also Wheel Lock.)
