Unlike the normal Kamaz, Heavy Kamaz is currently only used by the Epsilon Army and is extremely rare to be seen. It is used for transporting bulk cargo such as main Barracuda component or nuclear materials, and quite slow, but it has the ability to crush infantry and even crush small vehicles. Heavy Kamaz's armor is also much stronger than the normal Kamaz, so that four Harriers are absolutely impossible to destroy a Heavy Kamaz (two Harriers are enough to destroy a normal Kamaz).
In the Covert Ops mission Gridlock, Heavy Kamaz are used to transport fuel from the Nuclear Reactors to the Rocket Launchpad-turned-nuke. Destroying a Heavy Kamaz will lengthen the timer before the nuke could fire, while letting one reach its destination will shorten the timer.