Incendiary bombs, also known as firebombs, were used as an effective bombing weapon in World War II [1]. The large bomb casing was filled with small sticks of incendiaries (bomblets), and 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 (e.g., German Terrorflieger) with the targeted populations, and more than a few shot-down aircrews were summarily executed by angry civilians upon capture.[citation needed] The Nazi regime began the campaign of incendiary bombings with the bombing of London in 1940-41, and reprisal was exacted by the Allies in the bombing of Dresden in World War II[citation needed], a major Nazi transport hub, and to a lesser degree the 1943 bombing of Hamburg, a war-material production site, and the firebombing of Tokyo remains a source of controversy to this day (though in the case of the latter, the effect on Tokyo's intentionally decentralized subcontractor war industry manufacturers was devastating).

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.

White Phosphorus (WP) bombs and shells are essentially incendiary devices, and can be used in an offensive anti-personnel role against enemy troop concentrations. WP is also used for signaling, smokescreens, 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 Nazi 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 mortarmen were sometimes summarily executed by German forces in reprisal.[citation needed] In both WWII and Korea, WP was found particularly useful in overcoming enemy human wave attacks.

Since white phosphorus can be used as a multipurpose device to mark targets, provide a smoke screen, or signal to friendly troops, it may not be covered by UN protocols on incendiary weapons when used in this fashion.[citation needed] Protocol III of the UN Convention on Conventional 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.

A variety of pyrophoric materials can be also 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.