Arm Cannon

Samus Aran's Arm Cannon is her primary weapon, capable of both energy-based and ballistic attacks. The arm cannon, as its name implies, is affixed to the Power Suit'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. Despite its complexity, in Metroid Prime 3: Corruption, the Arm Cannon can only handle one beam at a time; she is unable to switch between beams throughout the course of the game. By default, Samus's Arm Cannon always features the Power Beam.

Though Samus's arm cannon is presumably of Chozo design, other species (as seen in Metroid Prime: Hunters) have Arm Cannons that can perform nearly identical functions. In the earliest years of the Federation, the Chozo built Samus Aran's arm cannon had the ability to change into a desired weapon. Soon, other Races began creating modular weapons like these.

Physical description
In the Prime Series, the Arm Cannon features many different configurations. The standard configuration, where the Cannon appears completely smooth, always represents the Power Beam. The wide configuration, where the sides of the Cannon expand, is used for the Wave, Light, and Nova Beams. The high configuration, where the top and bottom pieces of the Cannon move vertically, 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 forward, 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 separates from the Arm Cannon and widens, is used only for the Zero Laser. In Metroid Prime: Hunters the Arm Cannon's configuration is not changed, however the orange part of the cannon does change color when using the other hunters' weapons.

It is also shown to have many other functions, such as uplinking with computers or other systems, welding, melee combat, and controlling Samus's 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 players in Super Smash Bros. Brawl when Samus sheds her Power Suit. The arm cannon's three rings are shock absorbers to deal with recoil.

In Metroid: Other M, the exterior of the Arm Cannon has 2 green circles to deliver energy on both sides.

The inside of the Arm Cannon is more simplistic and is simply a long, narrow tube with some sort of trigger mechanism at the end, into which Samus inserts her hand. It can only be seen when using the X-Ray Visor because other visors cannot look through the solid Arm Cannon. The opening scene for Metroid: Other M shows what the inside of the arm cannon's barrel looks like and what happens when a beam is fired, and Metroid Prime Trilogy shows another, alternative look during the start up video and through to the game selection.

Beam weapons

 * Power Beam
 * Charge Beam (Overblast)
 * 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
 * Nova Beam
 * Hyper Beam (Hypermode)
 * Diffusion 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

Ultimate Power

 * Omega Cannon

Official Metroid Prime website
"Weapon effect: Devastating potential

Weapon range: 3-10 m

Weapon potential: Lethal

''The Arm Cannon is Samus Aran's primary offensive weapon. Built into the right arm of the Power Suit, the Arm Cannon is upgradeable with a variety of weapons, including the Wave Beam, Ice Beam and others. When used in combination with secondary weapons such as missiles, the Arm Cannon can become a devastating offensive tool."''

Trivia

 * A common misconception among new fans of the Metroid series, as with Samus' gender and name, is that the Arm Cannon is a replacement arm for Samus.
 * The Arm Cannon is an unlockable weapon in Phantasy Star Ø for the Nintendo DS.
 * The X-Ray Visor, when activated, allows Samus' hand inside the Arm Cannon to be seen. In Metroid Prime, Samus uses her hand to change configurations by changing her finger positions. While in Metroid Prime 3: Corruption, Samus can be seen pulling some kind of trigger with her index finger to fire.
 * In Corruption, after performing some interface while equipped with only the Power Beam, the Arm Cannon will seemingly "phase out" but will return to its original position shortly.
 * In Corruption, the Arm Cannon is the only part of Samus' suit that does not get recolored by Phazon as her corruption progresses. The Arm Cannon only ever shows signs of Phazon changes when using Hypermode.
 * As seen in the first concept art gallery, the Metroid Prime Wave Beam configuration was initially intended for the Plasma Beam, and vice versa.
 * In Prime, if Samus is idle and waits long enough she will flip a panel with four lights that show the colors of the game's four beams.
 * The Arm Cannon is one of the Power Suit pieces that can be picked up and thrown at other characters in Super Smash Bros. Brawl after performing the Zero Laser with the Power Suit torn apart.
 * In the Wii versions of Metroid Prime, it is possible to see Samus' hand when she changes beams while pointing the cannon upwards.
 * In many Prime cutscenes, the Arm Cannon is revealed to be rifled on the inside. This makes little sense, as all of her Beams are energy based (rifling is used to give a spin to bullets/grenades in order to make them fly straight). It may be used for her Missiles, but they also do not require rifling. Missiles have small wings to keep them flying straight (or guiding them while homing), although Super Missiles are bulb shaped and do not have wings in some of the games.