Napalm is an incendiary weapon that turns ordinary fuel into a sticky, slow-burning gel capable of clinging to surfaces and skin. First created in 1942, it became one of the most devastating weapons of the 20th century, used extensively in World War II, the Korean War, and the Vietnam War.
How Napalm Works
At its core, napalm is simply thickened fuel. Regular gasoline splashes and burns out quickly. Napalm clings to whatever it touches and keeps burning. The key innovation was finding a way to turn liquid fuel into a gel that sticks on contact, burns longer, and spreads across a wider area than any ordinary fire.
The original formula used aluminum soaps, compounds made from a mixture of coconut oil, naphthenic, and oleic acids, to thicken gasoline. These aluminum soaps are remarkably efficient thickeners. At concentrations as low as 0.3%, they can increase the viscosity of hydrocarbons by a factor of 30. The soap molecules form tiny spherical structures called micelles in the fuel, and these micelles clump together into a dense network that transforms the liquid into a gel. The name “napalm” itself is a shortening of naphthenic and palmitic acids, two of the original ingredients.
Napalm burns at roughly the same temperature as the fuel it contains, typically gasoline. What makes it so destructive isn’t an unusually high temperature but the combination of adhesion and burn time. A splash of gasoline burns for seconds. Napalm sticks and burns for minutes.
The Original Formula vs. Napalm-B
The version used in World War II relied on those aluminum soap gelling agents mixed into gasoline. It worked, but it had limitations: the soap could degrade over time, and the gel wasn’t always consistent.
By the Vietnam War era, the military had switched to Napalm-B, a reformulated version with a completely different chemistry. Napalm-B contained 50% polystyrene (the same plastic used in disposable cups and packaging foam), 25% benzene, and 25% gasoline. The polystyrene dissolved in the benzene and gasoline to create a thicker, more reliable gel that burned longer and was harder to remove from skin. This newer formula was also more stable in storage and easier to manufacture at scale. The U.S. military dropped up to 400,000 tons of Napalm-B during the Vietnam War alone.
Why It Causes Such Severe Injuries
Napalm inflicts damage through three mechanisms working simultaneously. The first is direct burns. Because the gel adheres to skin and clothing, victims can’t simply brush it off or roll to extinguish it the way they might with a normal fire. The burning gel maintains contact with tissue for far longer than splashed fuel would, causing deep burns that can reach bone.
The second mechanism is oxygen depletion. Burning napalm rapidly consumes oxygen in the surrounding area. In enclosed or semi-enclosed spaces, this can cause loss of consciousness and death by asphyxiation within minutes, even for people not directly touched by the fire itself.
The third is carbon monoxide and toxic gas production. Like any large-scale combustion of petroleum products, burning napalm releases carbon monoxide and other toxic byproducts that poison the air well beyond the immediate fire zone. The combination of extreme heat, adhesion, oxygen depletion, and toxic fumes made napalm one of the most feared weapons in modern warfare.
Origins at Harvard
Napalm was created on Valentine’s Day 1942 in a secret war research laboratory at Harvard University. Chemist Louis Fieser and his team developed the formula specifically to create an incendiary gel that would be effective against structures. It was explicitly designed with civilian infrastructure in mind and was even tested on mock-ups of German and Japanese houses to evaluate how well it could ignite residential buildings. The weapon moved from laboratory to battlefield remarkably quickly, seeing widespread use by 1944 in both the European and Pacific theaters of World War II.
Its use expanded during the Korean War and reached its peak during the Vietnam War, where napalm strikes against both military and civilian targets became a defining and deeply controversial feature of the conflict. The 1972 photograph of nine-year-old Phan Thi Kim Phuc running from a napalm attack became one of the most recognized images of the 20th century and intensified global opposition to the weapon.
International Legal Status
Protocol III of the United Nations Convention on Certain Conventional Weapons, adopted in 1980, prohibits the use of incendiary weapons against civilians under all circumstances. The protocol specifically targets weapons designed to cause burn injuries or set fire to objects, which includes napalm by definition.
The treaty has significant gaps, though. It restricts the use of air-dropped incendiary weapons against military targets located near civilian populations, but ground-launched incendiary weapons face fewer restrictions. And notably, several major military powers either haven’t signed the protocol or have signed with reservations that limit its practical enforcement. The United States signed the broader convention but did not ratify Protocol III until 2009, and even then with interpretive declarations.
What Replaced It
Most modern militaries no longer stockpile napalm in its classic form. The U.S. military destroyed its last napalm stocks in 2001. In its place, thermobaric weapons and other fuel-air explosives have taken on some of the tactical roles napalm once filled, using different mechanisms to achieve area-denial and anti-personnel effects. White phosphorus munitions, which the U.S. Department of Defense officially classifies as marking, illumination, or smoke-screening tools, also produce severe burns and have drawn comparisons to napalm, though their stated primary purpose is not incendiary.
The shift away from napalm reflects both changing military doctrine and the political cost of using a weapon so strongly associated with civilian suffering. The images from Vietnam made “napalm” a word that carries moral weight far beyond its chemistry.