Because ships were built primarily of combustible materials (wood, cloth, hemp, and pitch), fire was a devastating weapon against them. The simplest way to set ships on fire was to fire flaming arrows or ballista bolts on an enemy ship, but choppy seas sometimes meant that aiming was difficult. A more radical solution thus lay in the use of old watercraft, decked out with combustible materials, and sent to drift into the enemy fleet, with the hope of hitting at least one or two and setting them ablaze. Vessels of this sort would normally be fairly large ships capable of carrying sufficient combustible materials, such as wood and old rags as well as chemicals such as oil, bitumen and sulphur to help maintain the combustive process during the course of the vessel's final voyage.