Early thermal weapons were devices or substances used in warfare during the classical and medieval periods (approx 8th century BC until the mid-16th century AD) which used heat or burning action to destroy or damage enemy personnel, fortifications or territories.
Incendiary devices were frequently used as projectiles during warfare, particularly during sieges and naval battles; some substances were boiled or heated to inflict damage by scalding or burning. Other substances relied on their chemical properties to inflict burns or damage. These weapons or devices could be used by individuals, manipulated by war machines, or utilised as army strategy.
The simplest, and most common, thermal projectiles were boiling water and hot sand, which could be poured over attacking personnel. Other anti-personnel weapons included the use of hot pitch, oil, resin, animal fat and other similar compounds. Smoke was used to confuse or drive off attackers. Substances such as quicklime and sulfur could be toxic and blinding.
Fire and incendiary weapons were used against enemy structures and territory, as well as personnel, sometimes on a massive scale. Large tracts of land, towns and villages were frequently destroyed as part of a scorched earth strategy. Incendiary mixtures, such as the oil-based Greek fire, could be launched by throwing machines or administered through a siphon. Sulfur- and oil-soaked materials were sometimes ignited and thrown at the enemy, or attached to spears, arrows and bolts and fired by hand or machine. Some siege techniques, such as mining and boring relied on combustibles and fire to complete the collapse of walls and structures.
Towards the latter part of the period, gunpowder was discovered, which increased the sophistication of the weapons, and led to the eventual development of the cannon and other firearms. Development of the early weapons has continued ever since, with a number of modern war weapons, such as napalm, flame throwers, and other explosives having direct roots in the original early thermal weapons. Fire-raising and other destructive strategies can still be seen in modern strategic bombing.
The destruction of enemy possessions and territory was a fundamental strategy of war, serving the dual purpose of punishment and deprivation of resources. Until the 5th century BC, the Greeks had little expertise in siege warfare and relied on a strategy of devastation to draw the enemy out; they destroyed crops, trees and houses. Centuries later, the Byzantines recommended this strategy, even though they had developed siege technology.
Fire was the easiest way of harrying and destroying territories, and could be done easily and quickly by small forces. It was a strategy put to good use by the Scots during the Wars of Independence; they repeatedly raided into northern England, firing much of the countryside until the whole region was transformed. King Edward II of England pursued one raiding party in 1327 by following the lights of burning villages.The tactics were replicated by England during the Hundred Years' War; fire became their chief weapon as they laid waste to the French countryside during lightning raids called chevauchées, in a form of economic warfare. One estimate records the destruction of over 2000 villages and castles during one raid in 1339.
As well as causing the destruction of lands, foods and belongings, fire could also be used to divert manpower. 13th century Mongol armies regularly sent out small detachments from their main forces to start grass fires and fire settlements as diversions.
Devastation by fire was not only used as an offensive tactic; some countries and armies employed 'scorched earth' policies on their own land to deprive invading armies of all food and forage. Robert I of Scotland reacted to the English invasion of 1322 by launching punitive and diversionary chevauchées into north-west England, then retreating to Culross, burning as he went the Scottish lands which lay in the path of the English army. The English ran out of food and had to abandon the campaign.
Such acts of aggression were not limited to wars against territorial enemies, but could form part of the strategies of conquest, subjugation and punishment of rebellion. Alexander the Great suppressed a revolt in Thebes, Greece in 335 BC, after which he ordered the city to be torched and laid waste. Alexander ordered (or allowed) a similar arson at Persepolis in 330 BC. It was a policy which was repeated throughout the period. Following his conquest of England in the 11th century, William I of England asserted his control of Northumbria by destructive campaigns throughout the region: "He ordered that crops and herds, tools and food should be burned to ashes. More than 100,000 people perished of hunger", reported Orderic Vitalis, a contemporary chronicler. It was a scene repeated the following century, during the anarchy of Stephen of England's reign. Civil war erupted between Stephen's supporters and those of the Empress Matilda, a rival claimant for the throne. The Gesta Stephani tells of the deeds of one of Stephen's supporters, Philip of Gloucester, by describing how he "raged in all directions with fire and sword, violence and plunder", reducing territory to "bare fields and dreadful desert".
Besieged forces would sometimes launch sorties in an attempt to fire the attackers camps or equipment. When Hugh Capet besieged Laon in 986–987, his troops became drunk one night, and Duke Charles's men sallied forth and torched the camp, forcing Hugh to abandon the siege.
However, like all weapons, fire-raising had its own dangers. In 651 Penda of Mercia attempted to win Bamburgh Castle by building a pyre at its base from planks, beams, wattle and thatch. The wind changed direction and the fire blew back on Penda's men, who had to abandon the attack. This fortuitous wind-change was credited to Saint Aidan, who saw the smoke from the Farne Islands and prayed for the defenders.
Most of the terms used for throwing machines were vague, and could refer to a number of specific engines, and all went through a number of changes and developments over the period. Among the most common were the ballista, mangonel and trebuchet. The ballista was developed from large crossbows and served as a catapult, which used a string-winding mechanism to fire a missile or bolt placed in a groove. Other giant crossbows were used throughout the period, and an "espringal", based on the ballista, which threw large bolts, was developed in the 13th century. Torsion-powered arrow firers had been used from 400 BC, and were adapted for stones. A mangonel had a wooden spoon-shaped arm, to hold a stone or object, which was manipulated under tension from a twisted rope. The trebuchet was an advanced development of the 12th or 13th century, which used a counter-weight to power the throwing arm, and was the major siege engine until the cannon became widespread.
As the tunnels were constructed, they would generally be supported by wooden beams and posts. Once the mine had been finished, the internal space was filled with combustibles, such as brushwood, firewood, resin, and other incendiary substances; once ignited, these would burn the supporting props, causing the mine to collapse, bringing down with it the structures lying above. From the 15th century, gunpowder was also used, although the aim remained to burn the props.
Defenders might sometimes dig counter-tunnels in order to reach the enemy's mines and launch an attack; frequently thermal weapons would be used to drive the besiegers from the tunnels.
Rather than undermining a structure, some besiegers used borers to drill holes in the outer walls in an effort to destroy them; such methods were more effective than rams on brick walls (which tended to absorb the shocks from the ram). Borers differed in size and mechanism, but a typical machine was made from a log of wood, tipped with iron and supported and driven by windlasses or ropes. Once a series of holes had been bored along the length of a wall, the holes were typically filled with rods of dry wood, saturated with sulfur or pitch and then ignited. Bellows could be used to encourage a blaze.
Another example occurred during the 886 Siege of Paris, when the Vikings filled three warships with combustible material and pulled them upriver in a failed attempt to destroy the Franks' fortified bridges. Fire ships containing straw and powder were also used during the Chinese Battle of Lake Poyang in 1363.
During an attack, castle or fortification defenders could launch or pour the substances on the heads of attackers below. This could be done over the battlements, but also through purpose-built holes such as machicolations and murder-holes. Indian records suggest smoke and fire was used defensively within a fortress to confuse and disorientate attackers; iron grills could also be heated and used to block passageways. During night attacks, defenders could drop lighted bundles over the walls so the enemy could be seen; Chinese and Muslim sources also describe the light gained by torches hung on the walls.
Stone was also susceptible to intense heat, which would cause it to crack and collapse. Byzantine sources recorded the demolition of stone structures caused by placing clay pots of burning charcoal at the base of walls moistened with vinegar or urine, and the 6th century treatise by an engineer in Justinian's army includes the lighting fires beneath the walls amongst its instructions for sieges.
Stone castles sometimes offered other inflammatory targets. During the Crusades, Muslim defenders frequently hung bundles of straw against their walls as buffers against stones and rams; in turn, the Crusader archers would set these alight with fire arrows.
Both attackers and defenders needed to be prepared for incendiary and thermal attack. When the Athenians besieged Syracuse in 416 BC they lost many siege engines to fire. The Syracusan ruler Dionysius I must have taken note of this success, for when he laid siege to Motya in 398 BC he organised special fire "brigades", who successfully doused the fires when his siege engines were bombarded.
Flaming arrows and crossbow bolts were used throughout the period. 15th Century writer Gutierre Diaz de Gamez witnessed a Spanish attack on the Moorish town of Oran in 1404 and later described how "During the most part of the night, the galleys did not cease from firing bolts and quarrells dipped in tar into the town, which is near the sea. The noise and the cries which came from the town were very great by reason of the havoc that was wrought.
A long iron crossbow-bolt probably designed to carry a fire cartridge was found in a 13th-14th century castle in Vladimir, Eastern Russia. Such large machine-thrown bolts were ideal for incendiary weapons. The Mongols used an "ox-bow" machine to throw bolts which had been dipped in burning pitch, with a range of 2500 paces.
Anna Comnena records that at the 1091 Battle of Levunium, lighted torches were fixed to spears.
The Chinese Song Dynasty created fire arrows - rockets attached to arrows and launched in mass through platforms, and later created rockets such as the huo long chu shui, a multistage rocket used in naval combat. Primitive rockets made from bamboo and leather were used by the Mongols, under Genghis Khan, but were inaccurate. However, the Fatamids used "Chinese arrows" from the 11th Century, which probably included saltpetre. The Mamluks experimented with a rocket-powered weapons described as "an egg which moves itself and burns.
The combustible liquid could be shot from catapults, and would burst into flames on impact. Siphons, frequently of copper, were also developed, first appearing in the 10th and 11th centuries. The siphons could shoot a blazing stream, which a 10th century Mesopotamian source claimed could engulf twelve men. Mardi bin Ali al-Tarsusi, who wrote a military manual for Saladin in the 12th century, suggested that "naft" could be placed inside blown eggshells, which could be thrown from horseback. From the 12th century, mouth-blown tubes were developed for use in mines.
Similar petroleum and bitumen-based incendiary mixtures had been known for centuries before the invention of Greek fire, but this new recipe created a blaze which was extremely difficult to extinguish. It burned on water, and was used effectively in naval warfare, although it was primarily an anti-personnel weapon rather than a ship-burner. It remained effective at sea even after its use had declined on land after the 13th century.
The Greek fire recipes continued to be developed over the centuries, and by the High Middle Ages was much more sophisticated than the early versions. Saltpetre (also called "Chinese salt") was added to the mixture in the Islamic world, and China developed a dry saltpetre mixture in the 12th century, which eventually became gunpowder.
Pouring-oil was used in a number of historic battles, and Josephus described its use at Jotapata in AD 67, saying "the oil did easily run down the whole body from head to foot, under their entire armour, and fed upon their flesh like flame itself."
Oil was usually used to create incendiary devices. The Roman-Byzantine armies of the 6th century created "fire-pots", oil-based incendiary weapons which could be launched by hand or with ballistae. During the siege at Montreuil-en-Bellay in 1147, a mixture of oils from nuts, cannabis and flax, was heated in iron containers, launched by mangonel, and burst into flames on impact. The Chinese made early grenades out of oil-soaked hemp and cotton, which were ignited and thrown by mangonels.
Another use of oil can be seen in the naval battle of La Rochelle during the Hundred Years' War; the Castilians sprayed oil on the decks of English ships then ignited it by shooting flaming arrows down.
Pitch was a base ingredient in many incendiary devices throughout the period. The Boeotians developed a fire machine, which they used against the Athenian wooden fortifications during the Battle of Delium in 424 BC. A cauldron of burning coals, pitch and sulfur was suspended at one end of a hollowed-out log and bellows were fixed to the other end. A similar mixture was used 900 years later by the Scots, when they dropped bales of wood, tar and sulfur by crane onto the English "sow" (a large protective shield covering the battering ram) at the 1319 siege of Berwick-upon-Tweed.
There were some intriguing uses of animal products; during the Siege of Paris in 886 AD, the Franks dropped bucket-loads of a hot mixture of pitch (or oil), wax and fish on the attacking Vikings; the mixture got under the armour and stuck to the skin. Konrad Kyeser's Bellifortis of 1405 describes a poisonous mixture of sulfur, tar and horses' hooves. Other incendiary ingredients included egg yolks, and pigeon and sheep droppings. Live insects were also used, to sting the enemy. 4th century BC writer Aeneas Tacticus suggested defenders should let wasps and bees into enemy mines, and jars of scorpions were sometimes fired during early bombardment in naval battles.
In 189 BC Ambracia was besieged by the Romans, who dug mines under the walls. The defenders filled a clay jar with chicken feathers, which they then lit, using bellows to blow the acrid smoke down the tunnel; unable to approach the pot due to defensive spears, the Romans were forced to abandon their workings.
Other substances smoked rather than flamed. Sacks of burning sulfur were effective at clearing enemy mines due to the toxic smoke produced. Any smoke could be used in small confines; the Greek military writer Aeneas Tacticus recommended burning wood and straw to drive out enemy sappers by the smoke.
The discovery of gunpowder was probably the product of centuries of alchemical experimentation. Saltpetre was known to the Chinese by the mid-1st century AD and there is strong evidence of the use of saltpetre and sulfur in various largely medicinal combinations. The impetus for the development of gunpowder weapons in China was increasing encroachment by tribes on its borders. In a separate development in Europe, Roger Bacon invented gunpowder in the mid 13th century, although the mixture was not very effective. The composition of gunpowder varied throughout the period, and did not settle into the current ratios of saltpetre, sulfur and coal until the 17th century.
The earliest known formula for gunpowder can be found in a Chinese work dating probably from the 800s. The Chinese wasted little time in applying it to warfare, and they produced a variety of gunpowder weapons, including flamethrowers, rockets, bombs, and mines, before inventing firearms.
The years 904–906 saw the use of incendiary projectiles called 'flying fires' (fei-huo). Needham (1986) argues that gunpowder was first used in warfare in China in 919 as a fuse for the ignition of another incendiary, Greek fire. Initially, gunpowder mixtures were utilised through traditional engines and throwing mechanisms; containers and grenades were thrown by mangonels and trebuchets, and explosive rockets and arrows were developed, along with gunpowder flamethrowers.
Like firearms, cannon are a descendant of the fire-lance, a gunpowder-filled tube used as a flamethrower; shrapnel was sometimes placed in the barrel so that it would fly out together with the flames. In due course, the proportion of saltpeter in the propellant was increased to increase its explosive power. To better withstand that explosive power, the paper and bamboo of which fire-lance barrels were originally made came to be replaced by metal. And to take full advantage of that power, the shrapnel came to be replaced by projectiles whose size and shape filled the barrel more closely. With this, we have the three basic features of the gun: a barrel made of metal, high-nitrate gunpowder, and a projectile which totally occludes the muzzle so that the powder charge exerts its full potential in propellant effect.
Firearms remained in use in China throughout the following centuries. Meanwhile, gunpowder and firearms spread elsewhere very quickly. Gunpowder seems to have been widely known by the 1200s. The Europeans, Arabs, and Koreans all obtained firearms in the 1300s. The Turks, Iranians, and Indians all got firearms no later than the 1400s, in each case directly or indirectly from the Europeans. The Japanese did not acquire firearms until the 1500s, and then from the Portuguese rather than the Chinese.
In 1326, the earliest known European picture of a gun appeared in a treatise entitled "Of the Majesty, Wisdom and Prudence of Kings." On February 11 of that same year, the Signoria of Florence appointed two officers to obtain canones de mettallo and ammunition for the town's defense. A reference from 1331 describes an attack mounted by two Germanic knights on Cividale del Friuli, using gunpowder weapons of some sort. Cannon were first used by the Muslims at Alicante in 1331, or Algeciras in 1343. The French raiding party that sacked and burned Southampton in 1338 brought with them a ribaudequin and 48 bolts (but only 3 pounds of gunpowder). The Battle of Crécy in 1346 was one of the first in Europe where cannons were used.
However, early cannon were not very effective, the main benefits being psychological, frightening men and horses. Short barrelled, large-calibre "bombards" were used up until the late 15th century in Europe, during which period they grew increasingly larger. In the mid-15th century, mortars also appeared. Various smaller weapons also existed, including the serpentine, ribaudequin and cropaudin. The powder was of poor quality and was used in small quantities – to prevent explosion of the barrel – so the effective range of these cannon was rarely more than 200–250m.
The barrels of the cannon were forged or cast, and each gun generally differed in calibre and length. Early powder resembled a paste, and tended to burn slowly. Its composition varied in different geographical areas, the powder of Europe being quite different to that used in the Islamic world. The projectiles used were generally stone balls for bombards and mortars. Forged iron balls were used in smaller-calibre cannon, and coated with lead to make them smooth. From the 15th century, cast iron balls were used, which caused great destruction. As they were denser than stone, even small balls could be destructive. Thus, cannon became smaller in calibre, and longer-barrels increased the range.
While the incidence of use dropped, towards the latter end of the Middle Ages the incendiary devices became more sophisticated, and the principle of wielding fire with sword remained present throughout the Early Modern and Modern periods; improving technology merely allowed the process to become more efficient.
Fire remained an extremely successful weapon. During naval warfare of the Napoleonic wars, "the one thing most likely to destroy a ship was fire". Sometimes the fires were merely a side effect of weapon technology. Early firearms proved incendiary in their use and could start fires. During the Peninsular War, both Talavera and Salamanca battlefields were wracked by tremendous grassfires, first started by the guns. At the Battle of Trafalgar, 1805, the French ship Achille caught fire when musket-flashes from her own men's guns set fire to the tar and grease on the sail rigging; the ship eventually exploded.
Smoke screens have continued to be used by attackers and defenders as a means of sowing confusion and hiding movements. During naval battles in the 18–19th centuries, shots were sometimes fired early so a defensive screen was erected before the ships converged, to spoil the aim of the enemy.
The incendiary liquids of the ancient and medieval periods were also developed, and have their modern equivalents. World War I saw the development of the flamethrower, a modern version of the Byzantine siphons, which used gas under pressure to squirt a mixture of inflammable oil and petrol, ignited by a burning taper. Technology improved throughout the twentieth century, and the latter half saw the development and use of napalm, an incendiary liquid formed in part from naphtha, which was the main ingredient of the Arabic "naft".
Flames continued to be used for defensive light until artificial lights were developed. At the Siege of Badajoz in 1812, the French defenders flung down burning "carcasses" of straw so that the attacking British might be seen. Like the sieges of old, the British were met by incendiary weapons, but now these took the form of explosive grenades, mines and powder barrels as well as the enemy's guns.
Specific weapons from the ancient and medieval periods continued to develop, and many have modern equivalents. Rocket technology, originally trialled by the Mongols, Indians and the Chinese, amongst others, was improved by the 19th century; one example was the incendiary Congreve rocket, which had a tail, a fuse, and a powder charge (saltpetre, sulfur and carbon) inside a hollow shell. Grenades continued to develop, although still retaining some aspects of their medieval equivalents. The grenades carried on board Royal Navy ships in the late 18th and early 19th century were constructed from hollow cast iron, filled with gunpowder; the fuse was a hollow wooden tube filled with combustible material. During World War I, grenades were still occasionally launched by ballistae.
The use of some weapons continued with little change. The Koreans used fire arrows against the Japanese at the Battle of Hansan Island in 1592. At Trafalgar, in 1805, the British ship Tonnant shot wads covered in sulfur, which set fire to the Algésiras. Fireships were used in later periods. In 1588, the English sent fireships loaded with gunpowder, pitch and tar amongst the anchored Spanish Armada; the Spanish fleet broke formation, setting them up for the later battle. The last battle under sail was the Battle of Navarino (1827), part of the Greek War of Independence, during which fireships were utilised by the Turks.
Chemical warfare had been experimented with during the early period with sulfur, quicklime (calcium oxide), and others, and developments continued. World War I saw many gases used, including the extremely effective sulfur mustard (mustard gas).