Heated shot

Heated shot is the heating of round shot before firing from muzzle-loading cannons. The purpose is for setting fire to enemy warships, buildings, or equipment. 
The use of hot shot dates back centuries. It was stopped when vessels armored with iron replaced wooden warships in the world's navies. It was a powerful weapon against wooden warships, where fire was always a hazard. It was mainly used on shore batteries and forts, due to the need for a special furnace to heat the shot. 
The use of heated shot from a ship was so dangerous, that it was against Royal Navy regulations. The American ship USS "Constitution" had a shot furnace installed, for hot shot to be fired.