Incendiary weapons, incendiary devices or incendiary bombs are bombs designed to start fires or destroy sensitive equipment, using materials such as napalm, thermite, chlorine trifluoride, or white phosphorus.
Development and use in World War I 
The first incendiary bombs to be dropped during World War I fell on coastal towns in the south west of England on the night of 18–19 January 1915. The small number of German bombs, also known as firebombs, were finned containers filled with kerosene and oil and wrapped with tar-covered rope. They were dropped from Zeppelin airships. On 8 September 1915, Zeppelin L-13 dropped a large number of firebombs, but even then the results were poor and they were generally ineffective in terms of the damage inflicted. They did, however, have a considerable effect on the morale of the civilian population of the United Kingdom.
Development and use in World War II 
Incendiary bombs were used extensively in World War II as an effective bombing weapon, often in a conjunction with high-explosive bombs. Many different configurations of incendiary bombs and a wide range of filling materials such as isobutyl methacrylate (IM) polymer, Napalm and similar jellied-petroleum formulae were used, many of them developed by the US Chemical Warfare Service. Different methods of delivery, e.g. small bombs, bomblet clusters and large bombs, were tested and implemented. For example, a large bomb casing was filled with small sticks of incendiary (bomblets); the casing was designed to open at altitude, scattering the bomblets in order to cover a wide area. An explosive charge would then ignite the incendiary material, often starting a raging fire. The fire would burn at extreme temperatures that could destroy most buildings made of wood or other combustible materials (buildings constructed of stone tend to resist incendiary destruction unless they are first blown open by high explosives).
Originally, incendiaries were developed in order to destroy the many small, decentralized war industries located (often intentionally) throughout vast tracts of city land in an effort to escape destruction by conventionally aimed high-explosive bombs. Nevertheless, the civilian destruction caused by such weapons quickly earned them a reputation as terror weapons with the targeted populations, and a number of shot-down aircrews (e.g., in German, Terrorflieger) were summarily executed by angry civilians upon capture. The Nazi regime began the campaign of incendiary bombings with the start of World War II with the bombing of Warsaw in World War II, and continued with the London Blitz and the bombing of Moscow, among other cities. Later, an extensive reprisal was exacted by the Allies in the strategic bombing campaign that lead to the annihilation of many German cities. In the Pacific War, during the last seven months of strategic bombing by B-29 Superfortresses in the airwar against Japan, a change to firebombing tactics resulted in some 500,000 Japanese deaths and 5 million more made homeless. Sixty-seven of Japan's largest cities lost significant area to incendiary attacks. The most deadly single bombing raid in all history was Operation Meetinghouse, an incendiary attack that killed some 100,000 Tokyo residents in one night.
The 4 lb (1.8 kg) incendiary bomb, developed by ICI, was the standard light incendiary bomb used by RAF Bomber Command in very large numbers, declining slightly in 1944 to 35.8 million bombs produced (the decline being due to more bombs arriving from the USA). It was the weapon of choice for the British dehousing plan. The bomb consisted of a hollow body made from aluminium-magnesium alloy with a cast iron/steel nose, and filled with thermite incendiary pellets. It was capable of burning for up to ten minutes. There was also a high explosive version and delayed high explosive versions (2–4 minutes) which were specifically designed to kill rescuers and firefighters. Other tactics consisted of using explosive bombs in the attack to fill the streets with craters and rubble, hindering rescue services.
Towards the end of World War Two, the British introduced a much improved 30 lb (14 kg) incendiary bomb, whose fall was retarded by a small parachute and on impact sent out an extremely hot flame for 15 ft (4.6 m); it burned for approximately two minutes. Articles in late 1944 claimed that the flame was so hot it could crumble a brick wall. And for propaganda purposes the RAF dubbed the new incendiary bomb the Superflamer. Very little else is known about this new incendiary bomb that came into operational service late in the war in the European theater. Around fifty-five million incendiary bombs were dropped on Germany by Avro Lancasters alone.
Many incendiary weapons developed and deployed during World War II were in the form of bombs and shells whose main incendiary component is white phosphorus (WP), and can be used in an offensive anti-personnel role against enemy troop concentrations, but WP is also used for signaling, smoke screens, and target-marking purposes. The U.S. Army and Marines used WP extensively in WWII and Korea for all three purposes, frequently using WP shells in large 4.2-inch chemical mortars. WP was widely credited by many Allied soldiers for breaking up numerous German infantry attacks and creating havoc among enemy troop concentrations during the latter part of WWII. The psychological impact of WP on the enemy was noted by many troop commanders in WWII, and captured 4.2-inch mortar men were sometimes summarily executed by German forces in reprisal. In both WWII and Korea, WP was found particularly useful in overcoming enemy human wave attacks.
Post World War II incendiary weapons 
Modern incendiary bombs usually contain thermite, made from aluminium and ferric oxide. The most effective formula is 25% aluminium and 75% iron oxide. It takes very high temperatures to ignite, but when alight, it can burn through solid steel. In WWII, such devices were employed in incendiary grenades to burn through heavy armor plate, or as a quick welding mechanism to destroy artillery and other complex machined weapons.
A variety of pyrophoric materials can also be used: Selected organometallic compounds, most often triethylaluminium, trimethylaluminium, and some other alkyl and aryl derivates of aluminium, magnesium, boron, zinc, sodium, and lithium, can be used. Thickened triethylaluminium, a napalm-like substance that ignites in contact with air, is known as thickened pyrophoric agent, or TPA.
During the Vietnam War, the U.S. Army developed the CBU-55, a cluster bomb incendiary fueled by propane, a weapon that was used only once in warfare. Napalm proper is no longer used by the United States, although the kerosene-fueled Mark 77 MOD 5 Firebomb is currently in use. The United States has confirmed the use of Mark 77s in Operation Iraqi Freedom.
Incendiary weapons and laws of warfare 
According to the Protocol III of the UN Convention on Conventional Weapons governing the use of incendiary weapons:
- prohibits the use of incendiary weapons against civilians (effectively a reaffirmation of the general prohibition on attacks against civilians in Additional Protocol I to the Geneva Conventions)
- prohibits the use of air-delivered incendiary weapons against military targets located within concentrations of civilians and loosely regulates the use of other types of incendiary weapons in such circumstances.
Protocol III states though that incendiary weapons do not include:
- Munitions which may have incidental incendiary effects, such as illuminates, tracers, smoke or signaling systems;
- Munitions designed to combine penetration, blast or fragmentation effects with an additional incendiary effect, such as armour-piercing projectiles, fragmentation shells, explosive bombs and similar combined-effects munitions in which the incendiary effect is not specifically designed to cause burn injury to persons, but to be used against military objectives, such as armoured vehicles, aircraft and installations or facilities.
Use by criminal and terrorist groups 
Incendiary devices have been used by criminal, terrorist and direct action groups to commit arson attacks on their targets. The Molotov cocktail is a classic incendiary device that has been used by insurrectionary anarchists and rioters.
See also 
- Bat bomb
- Early thermal weapons
- Fire accelerant
- Flame fougasse
- Greek fire
- High explosive incendiary (HEI)
- Incendiary ammunition
- Meng Huo You (Historic Chinese incendiary weapon)
- Molotov cocktail
- Pen Huo Qi (Historic Chinese flamethrower)
- Stinkpot (Historic Chinese incendiary weapon)
- Wilbur Cross, "Zeppelins of World War I" page 35, published 1991 Paragon House ISBN I-56619-390-7
- World War II Guide.
- Popular Science, May 1945: "How we fight Japan with fire"
- "SUPERFLAMER Dropped by Chute Throws Fire 15 Feet." Popular Mechanics, December 1944, p. 13. Article bottom of page.
- Alan Dawson, 55 Days: The Fall of South Vietnam (Prentice-Hall 1977).
- although the 4th Geneva Convention, Part 3, Article 1, Section 28 states "The presence of a protected person(s) may not be used to render certain points or areas immune from military operations."
|Wikimedia Commons has media related to: Incendiary weapons|
- United States Strategic Bombing Survey (Pacific War) 1946
- Fire From The Sky 1944 article on the production of incendiary bombs
- AN-M50-series incendiary bombs (german)