Napalm grenade

The Napalm Grenade was a type of incendiary grenade used by UNSC forces during 2552. Not much is known about them, other than that they were used by Colonel James Ackerson in testing the MJOLNIR Mark V armor on Reach, hidden amongst the Pillars of Loki and used in conjunction with Sonic Grenades.

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

 * In the real world, 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.
 * The Type-3 Grenade, used primarily by Brute Stalkers in Halo 3 and Halo 3: ODST is possibly similar in function to a napalm grenade.
 * Despite it being mentioned that it was used in the Battle of Reach, it will likely not appear in Halo: Reach, due to Bungie stating that the only grenades that would appear in the game would be the Plasma Grenade and Fragmentation Grenade.

Links

 * Napalm on Wikipedia