From Halopedia, the Halo wiki
For the full list of weapons see Category:Weapons.
Human weapons tend to use bullets, explosives, coil/rail guns and lasers. Covenant weapons are generally plasma or energy based. Brute weapons use spikes or explosives. All plasma weapons use charge. All weapons run out of ammunition or charge when used extensively. Plasma weapons typically overheat if fired continuously for long periods of time, which causes the player's weapon to become temporarily unresponsive while it cools down.
An extensive array of weapons are available within the gameplay, with each weapon operating differently. This allows players to take different approaches and sometimes forces a change in tactics depending on the strengths and weaknesses of each weapon. Each player will also find a weapon to suit his or her tastes, in terms of power, speed, range, kickback and/or feedback.
Halo: Combat Evolved limited the number of weapons players could carry to two (of which only one could be used at any one time), forcing players to carefully select their preferred armament. Players fight with ranged and melee attacks, as well as a limited number of grenades. Bungie refers to the "weapons-grenades-melee" format as the "Golden Triangle of Halo", which has remained fundamentally unchanged throughout the trilogy. The player character's health is measured in both hit points and a continually recharging energy shield. The energy shield absorbs a significant portion of enemy fire until it becomes depleted, after which the player character will sustain damage, potentially causing death.
Halo 2 introduced new gameplay elements, most notably the ability to hold and fire two weapons simultaneously, known as "dual wielding". The health system was altered in this game, with the player no longer having hit points as well as shields. Also, the Assault Rifle was not included in this game.
Halo 3 adds to the series new weapons, and a class of items called equipment. The Assault Rifle returns in this incarnation, albeit with a decreased magazine capacity, but with more damage per hit.
Halo 3: ODST adds sound-suppressed weapons, namely the Silenced SMG and the Silenced Pistol, which replaces the Battle Rifle from Halo 3. Also, the game does not contain dual wielding, and Equipment is no longer usable by players; Equipment can now only be used by enemy brutes. Halo 3: ODST also marks the return of the Brute Plasma Rifle, replacing the regular version, and is also used by Drones.
Halo Reach replaces quite a few weapons with different variants, like the DMR, replacing the BR, and the Needle Rifle replacing the Carbine from Halo 2 and Halo 3. It also goes over a massive overhaul with the Assault Rifle, as it is now an MA37 rather than an MA5B. It also adds a play off of equipment called Armor Abilities. These can be used repeatedly with a brief "cool down" time added.
Halo 5: Guardians introduces variants of weapons in the game: for loadout weapons, these include attachments like Kinetic Bolts and Stabilization Jets, as well as new scopes (e.g. Morph sight, Hybrid sight); and for power weapons, there are usually two upgraded variants, an improved one and an advanced one. Mythic weapons are also introduced, with these weapons being extremely rare but powerful and historically significant (e.g. Oathsworn by Kelly-087, Nornfang by Linda-058). The new weapons introduced are the Plasma Caster, which replaces the Concussion Rifle, and the Hydra Launcher, which is a spiritual successor to the Plasma Launcher. All of the Forerunner weapons have been drastically overhauled as well.
The typical arrow cursor is hidden within gameplay, and replaced with a blue targeting reticle that stays locked to the center of the screen, when in first person and third person views. The reticle turns red when a shot will hit an enemy target, and green for allies.
Many weapons are scoped and have the capability to zoom 2× or 5× into any area, with some long range weapons even capable of reaching up to 10× magnification such as the Sniper Rifle. These always show the reticle and continue scoping after shots are fired.
While wielding non-scoped weapons, the player's armor has the capability to zoom, to a minimal extent. These hide the reticle when in the zoomed view, returning to the normal view after every shot, making them inefficient for sniping. However, skilled players can use this in online gameplay to keep a good eye on enemies or destinations. In Halo 5: Guardians, the smart scope feature is introduced, allowing players to increase the accuracy or range of all their weapons.
The types of available weapons follow the basic standards present in real life; Assault, Battle, and Sniping.
Grenades are frequently made available, primarily for anti-infantry combat. Some grenades can stick and some grenades are stronger than others.
Melee attacks are always available; if the player is able to get in range of an enemy, that can cause heavy damage. And melee attacks are very dangerous when you hit an enemy in the back, this will kill almost any enemy. Most times, a single melee attack is sufficient to completely deplete an enemy's shields. These are also used to take control of an enemy vehicle, by Melee attacking the craft, then planting a grenade to kill its driver.
Heavy weapons, such as turrets, are also present within Halo levels, either stationary, or mounted on Vehicles. Some turrets can be removed from their stands and used as hand held Support Weapons, but it makes the player move slower and gives the turrets limited ammunition. Only when driving a vehicle, controlling the Flamethrower, and controlling a turret, does the game switch into third-person view. Some vehicles, such as the Type-32/Type-54 Ghost, Scorpion Tank, and Banshee allow the driver to directly control mounted weapons while driving the vehicle. Other multi-occupant vehicles such as the Warthog require the player to remain in the weapon seat to control fire, and driving seat to control navigation.
Within campaign levels, the player's character (Master Chief, the Arbiter, any members of Buck's squad (excluding Veronica), Noble Six, Blue Team, or Fireteam Osiris, depending on the game played) usually begins with two weapons, and will always have access to weapons lying around, either near corpses or within weapon caches and stores.
Killed enemies or allies can be robbed of their dropped weapons as well. In Halo 2 and every game that follows, the player can exchange weapons with allied AI when requested, making it unnecessary to kill them only to use their weapons, although grenades still cannot be traded. In Halo 5: Guardians, John-117 or Jameson Locke can order AI-controlled Spartans to pick up weapons. However, AI-controlled Spartans can never drop their weapons upon death.
Weapons can be reloaded by collecting ammunition or swapping the player character's weapon with a loaded dropped weapon. If the player is already wielding the same weapon, they can swap if the new weapon is loaded or charged more than the wielded weapon.
Certain weapon types usually have more or less ammunition available. For instance, sniper rifles typically have less ammunition lying around then assault or battle rifles, which are intended as primary/multipurpose weapons.
The Marathon symbol can be observed on many human weapons in Halo games published by Bungie, it is very small and often blends in, and it is better observed very zoomed in. For example, it can be found being on the butt of the MA5C Assault Rifle, it can also be found on the Sniper Rifle near to the gun's trigger. They are all best observed in the Halo Encyclopedia.