It's the model from the Assault on Black Reach box set, and is therefore armed with a Multi-melta and Storm Bolter, and a Dreadnought Close Combat weapon.
Being a Walker unit, it moves the same was as Infantry which means it can traverse Dangerous and Difficult terrain the same way, which allows it to enter buildings and other areas where traditional vehicles cannot go.
It can move and fire both weapons, and is most useful in an anti-vehicle or monstrous creature role due to the Multi-melta which gives it a 24" range S8 AP1 shot (with an 2D6+8 for vehicle armour pen. if within half range.)
It has a decent front armour of 12, which all shots are directed against to represent the manoeuvrability of the machine, never retreats from assaults, and can perform Death or Glory! against other vehicles that attempt to Ram it. (A Dreadnought punching out an enemy tank makes me chuckle..)
It is equipped with Smoke Launchers and a Searchlight, neither of which have been modelled on yet, but they will be later when I've found some parts.
In games with no vehicles or other units worth hitting with the Multi-melta, it makes a great tar-pit for large units of fearless but weak infantry (I'm looking at you Termagaunts...) where it cannot be harmed as the minimum Strength needed to Glance the Dreadnought is 6, and can, if it hits, auto kill 4 enemy per player turn. (until the savvy Tyranid player realises that all he need do is move his Synapse Creatures out of range, removing the Gaunts Fearless rule and sending them scampering for cover. That's not happened yet though!)
