Vulcan is the name given to two weapons (at least, in VS manuals)
First is the Laser Vulcan. See enclosed link for details,
Second, the only weapon of the GAN-36 pilot. This weapon is called a Vulcan in the corresponding VS manual. This Vulcan is the correct weapon to bear the name Vulcan. However it acts completely differently from the 'mistakenly named' Vulcan (an autocannon, as specified below), with fast rate of fire and similar power to a VS Gatling Gun. This weapon is often called a Chain Gun (in fact it is even called this in this wiki). This can be taken to reinforce the view that the GAF-15D Vulcan (outlined below) has been given the wrong name.
The mistakenly named Vulcan
The right weapon of the GAF-15D pilot is Called a "Vulcan". This weapon appears alongside the shotgun auxiliary weapon and appears to be an autocannon auxiliary weapon (and acts like one) but is called "Vulcan" in the GAF-1D's (pilot) VS manual. It is very likely (almost definite) THIS IS A MISTAKE and this should therefore be dismissed as false until it is known for certain, therefore the Vulcan is considered to be an Autocannon (see appropriate page).