A CANNON is a large, usually mounted, gun that fires explosive shells. It has been used as a war weapon since the 15th century. A MINE is an explosive device placed under or on the ground and designed to destroy or disable enemy targets, typically by means of a shock wave and shrapnel. Mines have been used in warfare since the 12th century. Napalm is a flammable liquid used in incendiary bombs and firebombs, which is ignited by an internal incendiary device and burns fiercely. Napalm was first used as a weapon during World War II.