UNSC Ground Flare

Ground Flares are elongated tubes filled with a chemical that is ignited to produce light.

Background
The UNSC issues red-burning ground flares, sometimes referred to as a "fusee", for several tasks. They are most often used to illuminate weapons caches, mark paths for friendly forces and to signal aircraft, such as Dropships or VTOL aircraft. They can also be used to mark locations for fire support, or as a crude flashlight of sorts. The red light produced is most likely from strontium nitrate, potassium nitrate, potassium perchlorate and a fuel such as sulfur, magnesium, aluminum, or polymeric resin.

Trivia

 * Ground flares can be seen in several locations throughout Halo 3, most notably on Sierra 117 inside the various tunnels.