This new weapon type is introduced in Lost Planet 2, but was present in the first game. However, it was not functional, so it served only as a decorative accessory. It has infinite ammo capacity and is installed on most VS's. To access it, you only need to press the LS and any of the 2 triggers. Unlike other weapons, apart from the turret gun, the auxiliary weapons never run out of ammo and do not need to be reloaded.
There are several types of auxiliary weapon. The most common is the autocannon, mounted on the GTT-01 Nida,the GTF-11 Drio, and on the GAF-15D Drion (please note that the pilots autocannon is called a Vulcan in the VS manual but this is a mistake as a Vulcan is apparently the GAN-36 pilots gun. This information comes from the VS manual as well) as the pilot's main gun and on either side of the gunners' seats. It has a moderate rate of fire at about 2 shots per second. It also has relatively low firepower: a single round from an infantry Machine Gun does twice as much damage as a shot from this Auxiliary Weapon. Although weak when compared to most other weapons, it still comes in handy as a decent weapon of last resort.
A second type is the small machine gun mounted on the PTX-140R Hardballer. It is about equal in strength, but fires faster, allowing it to do slightly more damage.
The PTX-140R also possesses a chainsaw-like sword called the VS Caliber that does heavy damage at the expense of high T-ENG consumption (as long as it is active).
The GAN-3AM Triseed mounts a saw blade and a double claw blade in its arms; their respective melee attacks can be chained together into deadly combos.
The GAF-15D Drion also has a shotgun (official name) auxiliary weapon alongside its autocannon one. This weapon has a slower rate of fire but is more powerful than the autocannon.
The GAH-42BS Bleed uses its arms to deliver lethal punches that can be chained together like the Triseed's arm blades.
The Akrid VS's use their respective Akrid mounts' inherent abilities; the Dongo Gear lashes out with its club-like claws and signature rolling attack, the Battle Neegal uses its extending tail to perform quick melee attacks with a long reach, and the Tencale 8 stomps on nearby foes and immobilizes them with adhesive bullets fired from its mouth.