Arm Cannon

Samus Aran's arm cannon is her primary weapon, allowing for both energy-based and ballistic attacks. The arm cannon, as its name implies, is affixed to Samus's right forearm. What separates the arm cannon from other firearms is its ability to access various weapons systems by quickly changing its configuration, thus eliminating the need for multiple (and sometimes bulky) guns. For example, during her time on Tallon IV, Samus could switch between four beam systems (not including the final beam), missiles, and four Charge Combos. By default, Samus's arm cannon always features the Power Beam.

Though Samus's is presumably of Chozo design, other species (as seen in Metroid Prime: Hunters) have arm cannons that can perform nearly identical functions.

Physical description
In the Prime trilogy, the arm cannon features six different configurations. The standard, closed configuration, where the cannon appears completely smooth, is always reserved for the Power Beam. The wide configuration, where the sides of the cannon expand, is used for the Wave Beam, Light Beam, and Nova Beam. The tall configuration, where the top piece of the cannon protrudes upwards, is used for the Ice Beam, Dark Beam, and Plasma Beam (though the Plasma Beam is only in this configuration in Metroid Prime 3: Corruption.) The long configuration, where the muzzle of the cannon extends outwards, is used for the Plasma Beam (only in Metroid Prime), and the Annihilator Beam. A fifth configuration, only seen in Corruption when Samus enters Hypermode, shows the cannon opening up in apparently the wide configuration, but with half-pipe like chutes on the sides, presumably for ventilation. In Prime the Phazon Beam expands the gun in all directions at once. The last configuration, where 4 parts of the arm cannon protrude in 4 directions, the tip of the cannon contracts and turns blue, and a ring seperates from the arm cannon and widens, is used only for the zero laser. It is also shown to have many other functions, such as uplinking with computers or other systems, welding, physical combat, and directing the Gunship. In the Prime series, it is occasionally shown to have colored buttons on the inside of the round section, when it flips open. The Arm Cannon can also be picked up and thrown by player in Super Smash Bros. Brawl when Samus sheds her Power Suit.

Logbook entry
Metroid Prime Hunters:"An essential part of SAMUS's POWER SUIT, the ARM CANNON is UPGRADABLE and adaptable to other weaponry. To fire the weapon, press the FIRE button, Switch weapons by tapping the weapon icons at the top of the touch screen."

Beam weapons

 * Power Beam
 * Charge Beam
 * Long Beam
 * Wide Beam
 * Spazer Beam
 * Wave Beam
 * Ice Beam
 * Plasma Beam
 * Hyper Beam
 * Phazon Beam
 * Dark Beam
 * Light Beam
 * Annihilator Beam
 * Electro Lob
 * Battlehammer
 * Volt Driver
 * Magmaul
 * Judicator
 * Shock Coil
 * Imperialist
 * Omega Cannon
 * Nova Beam
 * Zero Laser

Ballistic systems

 * Missile
 * Ice Missile
 * Diffusion Missile
 * Super Missile1
 * Seeker Missile
 * Hyper Missile

Charge combos

 * Super Missile1
 * Wavebuster
 * Ice Spreader
 * Flamethrower
 * Darkburst
 * Sunburst
 * Sonic Boom

Other

 * Grapple Beam