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 Series, 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 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 colors when using the other hunters' weapons.

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 players in Super Smash Bros. Brawl when Samus sheds her Power Suit. The arm cannon's three rings are shock absorbers.

The interior 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 trailer 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.

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 (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
 * Omega Cannon
 * 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

 * Grappling Beam

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

 * 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 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 when Samus is in her Zero Suit.