Appearing about 240 BC, incendiary pigs were an interesting weapon thought to have been utilized in ancient Roman warfare. The concept was to cover the pig in tar and a flammable substance and, when lured close enough to the advancing or defending enemy the pigs would then be lit on fire. The hope was that the pigs would run uncontrollably into the ranks of the opposing force, causing a certain level of confusion. In any event, the idea was to make use of the weapon as a psychological tool to harass or scare the enemy into submission, or break his concentration at the very least.
Eventually the pig would either die of the excruciating pain of being burned alive or be killed by the oncoming enemy. This weapon of ancient warfare was extremely time sensitive so handlers would have to work fast to make the effort worthwhile.
It is suggested that this weapon concept was found to be most useful against other livestock such as horses and the mighty war elephants, as any bit of confusion and damage from fire could set these animals off in the wrong direction in a flurry.
As inhumane as the thought of setting live animals on fire was, the art of ancient warfare in terms of ranged weapons (limited then to arrows, spears, slings and catapults), could still be thought of as in its infancy. The idea of incendiary pigs, even in concept, must not have been an overly effective or accurate form of ranged psychological warfare as its use is not mentioned often.
Though no official records exist of incendiary pigs being used in combat practice such as this, a few writings by Pliny the Elder touch on the idea. Chinese lore also includes the concept of incendiary monkeys as a battlefield weapon. Anti-tank dogs were reported to have been used by the Soviet Union to combat invading German Armor at close range. Obviously, the idea of utilizing animals in place of humans in warfare was a beneficial one to any army.