“Those things are scary as hell. Ya hear that weird 'whump' sound and even if ya see it comin', you're transfixed, these big green blobs flying at you throwin' off sparks!”
The Type-33 Light Anti-Armor Weapon.  more commonly known as the Fuel Rod Gun or Fuel Rod Cannon. is a Covenant shoulder-fired mortar/radiation weapon.
A fuel rod gun schematic as seen in Halo: Combat Evolved .
A blueprint of the fuel rod gun in Halo: Reach .
The Fuel Rod Gun is a man-portable version of the cannon that is mounted on Covenant vehicles; it is a support weapon that is commonly employed in both anti-personnel and anti-vehicle roles. It appears to be recoil-operated and fires 3.8 cm explosive ballistic incendiary gel projectiles that travel to the target in a parabolic arc.
The design of the fuel rod gun is unique, resembling a large ornament more than a deadly weapon. The body of the weapon is typically black and covered by thick gold plates. Ammunition is loaded into a slot on top of the weapon nearest the user's shoulder, and can hold 5 ballistic projectiles. Because of the weapon's visibility, it is equally effective as a psychological weapon; due to the threat it represents, however, this means that soldiers will often ignore closer, more obvious targets in order to eliminate a Type-33 and its operator.
The Fuel Rod Gun is unique in the way it operates. Its ammunition is placed one on top of the other to form a magazine and then is loaded into the weapon; it is unknown what exactly holds the rods together. When the large "trigger" is pulled, the weapon ejects the projectile at high speeds. It can be assumed that the instant the projectile leaves the barrel of the weapon, the large flash associated with firing the fuel rod gun destroys the caps that are on each end of the fuel rod projectile. The rods are equipped with an activation delay that protects the wielder from explosions caused by carelessly firing fuel rods into nearby objects or in close quarters, however a fuel rod will detonate if they are fired into enemies at point-blank range. The fuel rod gun is used by most Covenant infantry; Type-33s are seen most often being wielded by Grunts. and, more rarely, by higher ranking Elites and Brutes as well. The Type-33 is extremely powerful, and as such the Covenant went to great lengths to ensure it does not fall into enemy hands - it was originally equipped with a fail-safe that would activate under certain conditions, either when the user drops the weapon without first engaging a safety or if the weapon runs out of ammunition and is not reloaded within a certain amount of time.  In late 2552. the fail-safe was removed, preventing the weapon from self-destructing, although it may be that some cannons were equipped with it and others were not. 
The Covenant fuel rod gun fires an unknown type of incendiary gel. Next to nothing is known about this type of ammunition except that when it strikes a target it does so with devastating results. When the fuel rod impacts an area or target, it is instantly subjected to temperatures similar to those caused by standard plasma weapon fire. The fuel rod gun shoots the same type of incendiary gel as the Hunters' assault cannons. Unlike the assault cannon, however, it
shoots canisters of the gel approximately 3.8 cm long instead of shooting globs of the material or concentrating its fire into a sustained beam.
The Fuel Rod Gun is an extremely devastating weapon in the hands of a skilled player. Its destructive power is so effective that human forces often focus all of their attention on infantry wielding the weapon. One strike from a fuel rod will instantly kill any light organic target, while infantry and light vehicles immediately outside of the kill radius are swatted away by the concussive force of the blast. The Fuel Rod Gun is highly effective against lightly armored vehicles as well, able to destroy them with only a few hits. The weapon takes less time to reload than the rocket launcher, holds more ammo in its magazine, has a slight tracking ability, and a higher rate of fire.
Rods from the fuel rod gun have a smaller explosive radius than the SPNKR. In addition, the fuel rods will arc once in flight and lose their accuracy over long distances, meaning players must compensate in order to strike their intended target. The large size of the weapon obscures the wielder's peripheral vision, and it reduces the speed of weaker infantry holding it, despite its extremely light weight, unless it is a Spartan or of course an Elite carrying the weapon, due to their superior strength. The Elites are strong enough that in Halo 3. they are capable of wielding the weapon with one hand. The bright color of the weapon makes the wielder easy to spot, even when the weapon is backpacked; the green flash that occurs when the weapon is fired, can also give away the user's position. The fuel rods are also extremely slow in flight. As a result, Fuel Rods are particularly weak against most reconnaissance vehicles (Ghosts, Warthogs, Banshees, Brute Choppers, Mongooses) at long range. This is because the intended target will easily dodge the fuel rod. It also lacks the lock-on and destructive capabilities of the Halo 2 rocket launcher or Halo 3 missile pod. Also, in Halo 3 and Halo: Reach. the fuel rods usually bounce off the ground, missing their intended targets, unless it is a direct hit or you are directly facing the surface, such as walls and even the Scarab's exterior, although very rarely it does ricochet off of vehicles, and obviously, infantry.
Hunters also brandish a variant of the fuel rod gun known as the assault cannon. It operates differently than the standard fuel rod weapon, specifically in that it is a select fire mode weapon capable of firing either fuel rod mortars or using the rod to generate a superheated beam. The cannon is integrated into the hunters' armor and cannot be removed. As such, it is unusable in any of the Halo games.
The fuel rod cannon is a vehicle-mounted variant of the regular infantry-issue fuel rod gun, and as such it is larger and more powerful. Examples of the fuel rod cannon include the Anti-Air wraith's primary weapon and the Banshee's secondary weapon.