A fire ship, used in the days of wooden rowed or sailing ships, was a ship filled with combustibles, deliberately set on fire and steered (or, where possible, allowed to drift) into an enemy fleet, in order to destroy ships, or to create panic and make the enemy break formation. Ships used as fire ships were usually old and worn out or purpose-built inexpensive vessels.
Warships of the age of sail were highly vulnerable to fire. Made of wood, with seams caulked with tar, ropes greased with fat, and stores of gunpowder, there was little that would not burn. Accidental fires destroyed many ships, so fire ships presented a terrifying threat.
With the wind in exactly the right direction a fire ship could be cast loose and allowed to drift onto its target, but in most battles fire ships were equipped with skeleton crews to steer the ship to the target (the crew were expected to abandon ship at the last moment and escape in the ship's boat). Fire ships were most devastating against fleets which were at anchor or otherwise restricted in movement. At sea, a well-handled ship could evade a fire ship and disable it with cannon fire.
Other tactics were to fire at the ship's boats and other vessels in the vicinity, so that the crew could not escape and therefore might decide not to ignite the ship, or to wait until the fire ship had been abandoned and then tow it aside with small maneuverable vessels.
During the period of the Crusades their use was frequent. Their use peaked during the 18th and 19th centuries, with fireships a permanent part of any naval fleet, ready to be deployed whenever necessary, such as the Battle of Tripoli Harbor.
