M90 shotgun

The M90 Close Assault Weapon System (CAWS), also known as the M90 Close Assault Shotgun, M90 assault shotgun, or simply the M90, is a pump-action shotgun in service with UNSC. It is a military variant of the prolific DTM series of shotguns from Weapon Systems Technologies.

Design
The M90 is a pump-action shotgun, chambered in the extremely powerful 8-gauge magnum shell, and feeding from a 12-round, dual-tubular, non-detachable magazine. It is generally utilized alongside MAG 15P-00B rounds,  and is designed as a more practical and cost-effective recreation of Misriah Armory’s M45E Tactical Shotgun,  though in UNSC service it is considered to be functionally identical.

The magazine of the weapon is prominently positioned above the barrel, with the weapon’s glowing iron sights mounted atop it and the receiver located just behind, facing upwards, roughly in-line with the trigger. The magazine possesses a dull grey or glossy black finish with ribbed indents along its length. A flashlight is integrated into the weapon’s forend, which also features a prominent reddish button.

Functionality
The M90 shotgun is hefted like a rifle, with the user's dominant hand holding the primary pistol grip, and their off-hand supporting the weapon by holding onto the forend (the portion of the weapon which is acted upon by the user to facilitate the pump action, which also acts as a forward grip for the off-hand). As is typical of human firearms, in order to discharge the weapon, the trigger positioned at the top of the pistol grip must be depressed. If the weapon is loaded with standard ammunition, the weapon's firing will take the form of a spray of pellets, referred to as "buckshot", which are quite powerful at close range but lose damage efficiency as the spray disperses and loses energy. The firing of the weapon produces a fiery muzzle flash as burning propellant gasses leave the barrel.

Once the chambered round is fired, to repeat, the forend of the weapon is slid back across the weapon’s underside in the direction of the stock, retracting the bolt and removing the spent shell from the firing chamber. When the forend is fully retracted, the spent shell will have been ejected, and the way will have been cleared for the elevator component to position a new round for the bolt to carry into the chamber when the slide is once again pushed forward in the direction of the muzzle. Once the weapon’s magazine is expended, new rounds must be inserted one at a time into the receiver to continue firing. It is possible at any time to top up the magazine with additional ammunition until it is full.

Performance
The M90 is a devastating weapon in close, confined environments, with a loud report and strong recoil. The spray of pellets from the weapon mean that at slightly longer ranges, it can be used to hit clusters of targets simultaneously, but also makes the weapon inefficient at extended ranges due to the low ratio of shot which hits the target to the amount of shot fired. The M90's powerful cartridge makes it capable of efficiently engaging and defeating enemies with energy shielding within effective range. The Covenant learned to be wary of this weapon in urban environments, noting its close-range lethality.

History
The M90 was a common close-range battle implement in the service of the UNSC throughout the Covenant War. It saw service in the hands of John-117 during Operation: SILENT STORM, but its most prominent usage came in 2552. It played a notable part in the Battle of Installation 04, being used by UNSC marines against the Covenant and Flood. An M90 was also present during the ensuing Skirmish over Threshold. It went on to be widely utilized during the Battle of Earth. Notably, the Master Gunnery Sergeant who oversaw John-117's issuing with his new MJOLNIR Mark VI armor was killed on Cairo Station while using an M90 to defend his armory from elites. M90s were brought on the UNSC In Amber Clad, and thus were employed throughout the Battle of Installation 05. During the battle, they were frequently captured and pressed into service by brutes.

Classic Depiction
The original Halo: Combat Evolved depiction is different in three notable aspects from the later depictions in Halo 2 and Halo 2: Anniversary. The first is that the weapon features a smooth magazine lacking the ribbed indentations, with a distinctive chrome finish. The second is that the iron sights glow blue instead of green. The final differentiation is that in Halo: Combat Evolved, but not successive depictions, when the weapon is reloaded after being completely emptied, the weapon’s action is worked to chamber the first round.

Trivia

 * In Halo: Combat Evolved, the M90 shotgun shares its reticule with the then-PC-exclusive flamethrower.
 * In the second issue of Halo: Fall of Reach - Boot Camp, the captain of the retrieves several shotguns from a cryo chamber. In the first two panels, the shotguns appear to be M45s, though they resemble M90s in subsequent panels.
 * In Halo 2: Anniversary, if the player uses Active Camouflage while the M90 is equipped, the shells will be the only objects still visible. This could be because the shells are technically not attached to the shotgun (like the magazines in other weapons) but rather held inside the weapon until ignited and fired. This is best seen when playing as the Arbiter.
 * In Halo: Combat Evolved, the shotgun is the most effective weapon in the game against most Flood forms. A single shot is capable of killing Flood combat forms and Flood carrier forms and works best when paired with a weapon with a high-rate of fire such as an MA5B assault rifle to deal with Flood infection forms. The shotgun is still effective in later games, but not to such a degree as, starting in Halo 2, infection forms can revive deceased combat forms unless the body is destroyed. Halo: Combat Evolved lacked this resuscitation ability for the Flood.

List of appearances

 * Halo: The Fall of Reach
 * Halo: Combat Evolved
 * Halo: The Flood
 * Halo: First Strike
 * Halo 2
 * Halo Graphic Novel
 * Breaking Quarantine
 * Halo Wars
 * Sadie's Story
 * Halo Legends
 * Homecoming
 * Origins
 * The Package
 * Halo: Blood Line
 * Halo: Fall of Reach
 * Boot Camp
 * Halo 2: Anniversary
 * Know Your Enemy
 * Halo Mythos
 * Halo Wars 2
 * Halo: Fireteam Raven
 * Halo: Silent Storm