Napalm was used in flamethrowers and firebombs by the U.S. and Allied forces. Napalm is made to burn at a specific rate and stick to materials. This is done by mixing different amounts of napalm and other materials. Another useful (and dangerous) effect, primarily involving its use in bombs, was that napalm "rapidly deoxygenates the available air." It also creates large amounts of carbon monoxide causing suffocation. Napalm bombs were also used in the Vietnam War to clear landing zones for helicopters.