Incendiary missiles, such as buckets or barrels filled with a fiercely burning composition, had been used from earliest times, long before cannon. These crude incendiaries survived through the 1700's as, for instance, the flaming cargoes of fire ships that were sent amidst the enemy fleet. But in the year 1672 there appeared an iron shell called a carcass (fig. 41), filled with pitch and other materials that burned at intense heat for about 8 minutes. The flame escaped through vents, three to five in number, around the fuze hole of the shell. The carcass was standard ammunition until smoothbores went out of use. The United States ordnance manual of 1861 lists carcasses for 12-, 18-, 24-, 32-, and 42-pounder guns as well as 8-, 10-, and 13-inch mortars.

During the late 1500's, the heating of iron cannon balls to serve as incendiaries was suggested, but not for another 200 years was the idea successfully carried out. Hot shot was nothing but round shot, heated to a red glow over a grate or in a furnace. It was fired from cannon at such inflammable targets as wooden ships or powder magazines. During the siege of Gibraltar in 1782, the British fired and destroyed a part of Spain's fleet with hot shot; and in United States seacoast forts shot furnaces were standard equipment during the first half of the 1800's. The little shot furnace at Castillo de San Marcos National Monument was built during the 1840's; a giant furnace of the mid-1860's still remains at Fort Jefferson National Monument.

Loading hot shot was not particularly dangerous. After the powder charge was in the gun with a dry wad in front of it, another wad of wet straw, or clay, was put into the barrel. When the cherry-red shot was rammed home, the wet wad prevented a premature explosion of the charge. According to the Ordnance Manual, the shot could cool in the gun without setting off the charge! Hot shot was superseded, about 1850, by Martin's shell, filled with molten iron.

The smoke shell appeared in 1681, but was never extensively used. Similarly, a form of gas projectile, called a "stink shell," was invented by a Confederate officer during the Civil War. Because of its "inhumanity," and probably because it was not thought valuable enough to offset its propaganda value to the enemy, it was not popular. These were the beginnings of the modem chemical shells.

In connection with chemical warfare, it is of interest to review the Hussite siege of Castle Karlstein, near Prague, in the first quarter of the fifteenth century. The Hussites emplaced 46 small cannon, 5 large cannon, and 5 catapults. The big guns would shoot once or twice a day, and the little ones from six to a dozen rounds.

Marble pillars from Prague churches furnished the cannonballs. Many projectiles for the catapults, however, were rotting carcasses and other filth, hurled over the castle walls to cause disease and break the morale of the besieged. But the intrepid defenders neutralized these "chemical bursts" with lime and arsenic. After firing 10,930 cannonballs, 932 stone fragments, 13 fire barrels, and 1,822 tons of filth, the Hussites gave up.