Assault cannon

The Hunter Fuel Rod Variant is a variant of the standard Fuel Rod Gun utilized only by the Hunters. It has two variants, one of which is all but identical to the normal Gun, the other of which is closer to the vehicle variant and fires a continuous beam.

Description
The weapon is incredibly heavy, making it suitable for the extremely strong Mgalekgolo or "Hunter". The only known instances of it are fused directly to the Hunter's armor, located on the right "arm" of the colony, built into the Lekgolo that make up the limb.

Firing Operation
The ammunition it uses is similar to that of the Fuel Rod Gun; tubes of radioactive incendiary gel or plasma. Tubes can be fired individually, which detonate on impact and have an arcing trajectory, or have the gel or plasma sprayed out of the weapon in a 'beam'. The weapon itself can switch between these two modes by the Mgalekgolo using it. However, before firing, the weapon must be charged up. This "charge" makes it extremely obvious that the Hunter is attempting to shoot you, and it also makes it fairly easy to dodge the cannon's blast in Halo:CE.

In terms of gameplay, the Hunter Fuel Rod has changed in each version of Halo, in terms of operation and aesthetics.

Firing Behavior
In Halo: Combat Evolved, it was only able to fire single shots, and appeared to contain its gel supply in a drum mounted underneath the arm. In Halo 2, there were minor changes to its appearance but the weapon fired a continuous stream rather than individual blasts while the "drum" reloaded and fired. In Halo 3, the Hunter Fuel Rod is aesthetically very different, but operates much the same as it does in Halo 2. The cannon in Halo 3 can be cut off instantaneously if the target has gone to cover, which stops it from wasting ammunition, but it also has a "force" effect where it blows away movable objects such as supply crates. Also, in Halo 3, the "claws" seem to have hinges, although they are never seen moving in gameplay.

Trivia
It resembles the back of the hunter if viewed from the top
 * In Halo:Combat Evolved, the Hunter Fuel Rod fired single fuel rod shots, whereas in both Halo 2 and Halo 3, it was capable of firing a continuous "beam". Also, the Halo 2 and Halo 3 beam is flexible, in the way that the beam can form a rough "S" when moved accordingly. Though it is generally accurate, the projectiles are slow and can be dodged easily.
 * It is speculated the Scarab's main gun is just an enlarged version of the Hunter Fuel Rod due to the similarities of the charge-up and the color of the beam.
 * In Halo: Combat Evolved, Hunters will not continue to track you once the cannon has started to charge, making the Hunters inaccurate with moving targets.
 * In Halo 3, if you look closely at a Hunters Assault Cannon when it is charging up, green electricity protrudes from the three parts jutting out of the weapon and they form together to make the beam of energy.
 * In Halo 2, the Assault Cannon looks similar to the one from Halo:CE, but with the addition of claws on the barrel, making it look a bit more menacing.
 * The Halo 3 variant doesn't contain the "drum" like the previous Assault Cannons. Instead it has 6 tubes on the side of the gun which appear to house the incendiary liquid.
 * In Halo CE, the hunter, strangely, will never hit a stationary target meaning that the original Assault Cannon's recoil severely lowers the accuracy of the said cannon. You can use this to your advantage to avoid being injured.
 * The green energy that forms when a hunter charges their weapon in Halo 3 makes the charge look almost like an overcharged plasma pistol.
 * The official novels refer to the Hunter Variant as a "Fuel Rod Gun" for those set prior to and during the events of Halo CE, and as the "Fuel Rod Cannon" for the others.
 * In Halo:CE, it was possible to trick two Hunters into firing at each other by standing between them. This is still possible in Halo 2 and Halo 3, but is more difficult to utilize because of the new beam properties of the weapon. Hunters could simply change their aim to hit the player.