Napalm grenade

In the Halo Universe, the Napalm Grenade was used by UNSC forces in the Halo Novels. It, however, is not in Halo 3, since its idea has been replaced by the Type-3 Grenade, used primarily by Brute Stalkers.

Background
Historically, Napalm is a mixture of chemicals which, when mixed with gasoline and compressed, makes a sticky incendiary gel. Developed by the U.S. in World War II by a team of Harvard chemists led by Louis Fieser, its name is a combination of its original ingredient's names:
 * Aluminum salts of naphthenic and palmitic acids.

The name has since evolved from just the gasoline and Napalm gel, to mean any substance that causes intense fires upon ignition.

Trivia

 * International law does not necessarily prohibit the use of napalm or other incendiaries against military targets. However, use against civilian populations was banned by the United Nations.