M319 grenade launcher

The M319 Individual Grenade Launcher, more formally known as the Individual Grenade Launcher, Caliber 40mm, M319, is a single-shot, break-action explosives launcher produced by Misriah Armory for use by the United Nations Space Command.

Design details
The M319 is is one of the most versatile grenade launchers in the UNSC arsenal, and has accordingly been a staple of the UNSC Army's infantry for decades. The weapon has a relatively simple design; a break-action design that allows a single grenade to be loaded into the breech and fired, before reloading again. The muzzle of the weapon has a bulkier frame surrounding the barrel, atop which two picatinny rails are mounted - one on the left and right sides, respectively - allowing for weapon attachments to be mounted onto the launcher. As standard, the weapon has a fold-down foregrip and a top-mounted carry handle. The top of the weapon frame additionally mounts a built-in sight post, with a reticule and a trajectory readout allowing the user to estimate the grenade arc once fired. As with most UNSC weapons, the weapon can be smart-linked with a heads-up display, allowing the reticule and trajectory information to be displayed inside a given helmet for easier operation.

The aft of the grenade launcher is stockless, meaning the weapon cannot be shoulder-fired. Mounted to the left side of the grip assembly is a small remote detonation system (shared with the M460 Automatic Grenade Launcher) consisting of a viewscreen displaying readout status on the weapon and the loaded munition. When fired, the launcher can display one of two behaviours; Once fired, the remote detonation system's screen updates to showcase the status of the fired grenade. While loaded and ready to fire, the screen displays "ARMED", indicating the weapon is ready to fire. Once fired, the readout briefly displays "LNKING" (presumably indicating it is connecting to the grenade), then to "IN AIR" or "LNKD" depending on fire mode, before finally displaying "BOOM!" upon detonation.
 * The first (and standard) launches a single grenade that detonates shortly after impact with a given target, allowing the grenade to bounce off a surface. This is accomplished by a single trigger pull.
 * The second firing mode, done by holding the trigger down once fired, primes an alternate fuse on the grenade that will not detonate until the user has released the trigger. This can be used strategically to allow for indirect fire, setting traps, or simply remotely-discharging the weapon. This can also serve as a dead man's trigger, with the grenade being detonated should the operator be killed.

Overall, the M319 has a centuries-long track record of service in the UNSC Army - something attributed to the weapon's rugged and reliable nature even in adverse conditions.

Ammunition
The M319 is capable of firing all standard lethal and nonlethal 40mm grenades in the UNSC inventory. The most commonly used are the MK110 MOD 2 HEDP (high explosive, dual-purpose) and the XM20P EMP warhead. While the Mk110 MOD 0 is simply a standard explosive munition, the XM20P is a versatile munition that is used to generate an electromagnetic pulse at the point of impact, similar to those emitted by the Covenant's plasma pistols and power drains. The XM20P's EMP effect is capable of stripping energy shielding and temporarily disabling vehicles, making it useful in augmenting a standard infantry unit's effectiveness against more hardened targets.

The grenades fired by the launcher emit a whistling sound while in the air, which can alert enemy forces to the presence of the projectile.

Variants

 * Pro Pipe: a specialised M319 variant equipping a laser targeter that allows the rounds to adjust their trajectory after firing to improve accuracy, similarly to the behaviour of the Forerunner Z-180 Scattershot.

Operational history
The M319's service history dates back three centuries to 2263; it was originally designed by a Misriah Armory team on Mars (presumably at their Eos Chasma facility), and soon became a staple weapon of the UNSC Army. In the centuries since its introduction, it has seen action in several armed conflicts including the Insurrection - during which it proved particularly effective. During the Human-Covenant War, it proved less effective against energy shielded Covenant foes, it could be used to deadly effect against unshielded targets.

Because of the weapon's reliability and power, it is expected to remain in Army service, and is still used by SPARTAN-IVs a tactical simulations and War Games.

Halo: Reach
"Area of effect weapon. Hold and release trigger for Alt. Fire; which disables most vehicles and shields."

- In-game tooltip.

Production notes
As can be seen in some early concept art, the M319 was originally planned to be a revolver type grenade launcher like the XM510 grenade launcher seen in Halo Wars. The artist who created this concept art, Isaac Hannaford, revealed that the design was changed to the current single-shot, breech-loaded design because the original was thought to have "too many grenades," which presumably might make it overpowered.

When the grenade launcher returned to the Halo games in Halo 5: Guardians' Monitor's Bounty update, an unused variant of the launcher known as the "Grenade Launcher CLUSTER" was kept within the game files. While viewable in Halo 5: Forge via modding, it is unusable in the game itself.

Trivia

 * The grenade launcher is commonly known as the "pro pipe", a reference to grenade launchers in other first-person shooters, primarily the Call of Duty series, which are collectively known as "noob tubes" due to their ease of use. This nomenclature lead to the naming of the REQ variant of the weapon.
 * In the Halo: Reach Multiplayer Beta, if a player fired the M319 and held the trigger until they died and someone else picked up the weapon, the player holding the M319 would take control of the dormant grenade.
 * When reloaded, the M319's operator does not extract an empty shell casing. This could mean that it uses a caseless grenade round or the round utilizes rocket propulsion, which can be supported by the fact that there is a fire trail extending from the back of a grenade in flight.
 * In the alpha build, the M319 had a red light on its side. This was removed in the beta build.
 * When the grenade is fired from the weapon and set to manual detonation, a skull and crossbones symbol will appear below the distance counter indicating the number of targets in its explosive radius.
 * In campaign, kills with the grenade launcher's secondary mode always reward the player with the EMP Blast Medal despite that some enemies, such as the Unggoy and Jiralhanae, do not possess energy shielding and therefore could not be affected by EMP blasts. Kills by impact or splash damage count as ordnance weapon kills.
 * In Halo 5: Guardians, the projectiles for both versions will explode upon impact with the target. Interestingly enough, this function was first seen in both Halo: Spartan Assault and Halo: Spartan Strike.
 * Sometimes, in Halo 5: Guardians, if the player is hit with an M319 grenade but does not die (e.g. being hit by a teammate in Super Fiesta matches), the player will hear an ear-ringing sound effect identical to what they hear when hurt with explosives in the solo campaign.

List of appearances

 * Halo: Reach
 * Halo 4
 * Halo: Spartan Assault
 * Halo: Spartan Strike
 * Halo: Ground Command
 * Halo 5: Guardians
 * Halo: Renegades