M319 grenade launcher

The M319 Individual Grenade Launcher, more formally known as the Individual Grenade Launcher, Caliber 40mm, M319, and humorously as the "Pro-Pipe", is a single-shot, break-action, explosives launcher in use by the United Nations Space Command, specifically the UNSC Army. It has been a mainstay weapon, due to its simplicity, ruggedness and firepower, in the UNSC Army since its adoption in 2263, and has seen action in several armed conflicts during nearly three centuries of use, with the Human-Covenant War as the most prominent. It was used during the Battle of Reach.

Design Details
The grenade launcher has two firing modes. The first launches grenades at around normal grenade speed, which detonates on impact with an opponent or after normal grenade time after hitting a non-opponent surface, in which case, the grenade will explode after bouncing off the ground once. The second firing mode shoots a grenade that explodes when the player wishes. This is performed by holding down the trigger, which fires the grenade but it is merely primed, it will only explode after the trigger is released. This enables the player to lay a trap and essentially creates an explosive with a dead-man's trigger (a trigger that will go off once it is released, e.g. when the player dies). Like the Halo: Reach Fragmentation grenade, a player will take damage if hit by the grenade when it is merely primed.

Also, the grenade acts as a form of EMP that could bring down or temporarily disable vehicles, but only when used in the firing mode that allows the player to fire the grenade in a dormant, primed state.

The weapon utilizes a break-action breech loading system, which after firing one round must be reloaded, like that of many twentieth century shotguns.

Trivia

 * The grenade launcher has multiple nicknames among the fan community and Bungie alike, including "pro-pipe", a reference to the numerous grenade launchers in first-person shooter games, which have been collectively dubbed "noob-tubes".
 * The M319 IGL being manufactured in 2263 makes it the oldest known active service weapon utilized by the UNSC.
 * A direct hit on an enemy's body can cause an instant kill. This is difficult to pull off except at very close range, where the M319 IGL can be used as an effective shotgun as long as the splash damage is avoided.
 * When fired from an extremly close range the grenade round will bounce off the enemy and instead explode near the player who fired it.