A Hovertank is a ground combat vehicle designed to engage the enemy with direct fire, with an emphasis on anti-vehicle weaponry, and which uses an Antigrav system to hover a few meters or less above the terrain.
Hovertanks are used extensively by the Light Infantry, as they are useful for both riot control and for securing the surface of a Bug-infested planet while the Tech Infantry goes down the tunnels to dig the Bugs out of their holes. A typical hovertank is armed with one or two main guns, which are either heavy railguns or some sort of plasma cannon or heavy chemlaser, intended to be used on vehicles, bunkers, and the larger castes of Arachnid; and one to several lighter anti-personnel weapons to use on enemy infantry or the smaller castes of Arachnid.
The most common models of hovertank used in the mid-2200's are the Mark III and Mark V hovertanks, both originally built for the Frontier Worlds Territory by Olin Industries, but later used by the Earth Federation and others as well. Both have been built with a bewildering array of different weapons system options and other add-ons.
Behind the Scenes
Hovertanks such as the Mark III were only added to the story to provide a clear technogical evolutionary predecessor to the Mobile Siege Fortresses seen in Treschi's plotline in Season 4.3, and designed with that purpose in mind. Originally, the TI universe was supposed to not use tanks, troopers in power armor filling that role in ground combat as one-man walking tanks. The Mark III hovertank was designed by Martin Hohner, and much later we stumbled upon the pic used above of a Mark V hovertank, labeled as such on someone else's website, which was close enough to our previously-designed Mark III that it could very easily be an improved variant.