The VRM, or Variable Range Missile, was developed by the Inner Sphere to provide mechwarriors with a flexible missile that has the potential of both the more powerful SRM and the MRM and it's greater range. Using a hybrid rocket engine, the VRM carries a liquid component to increase the thrust of the engine, or alternatively boost up the yeld of the warhead. However, the liquid is a volatile as inferno gel, which makes the VRMs go off as easily as an inferno missile. Additionally, the missile uses a copperhead guidance system tied to a TAG laser the firing unit needs to mark the intended target (the consumption of the liquid as rocket fuel destabilizes the missile in midflight so much that conventional guidance systems were useless).
A unit carrying VRMs needs to carry a TAG unit as well, which has to sare the same firing arc as the missile launcher firing the VRMs. If the TAG pod is destroyed, the VRMs may not be fired anymore. The VRM weighs 10 kg and can be fired with either SRM or MML racks (which maximizes the flexibility).

BTW: this is the second pic I made with my new graphics tablet, and the very first one I didn't have a sketch for. And I like it. ^_^