This post is the time for the Dreadnoughts to make an appearance. I love the little dinky EPIC Dreadnought models, they are so characterful and look so cute! Sadly this attraction does not really follow through to Dreadnoughts in the game – they are a somewhat awkward combination of rules and availability. As a 15cm speed Armoured Vehicle they restrict any formation they are attached to to walking speed, which means that they cannot feasibly be using their free Rhinos, but it means stands in contact with them will be able to claim cover. They then have CC4+, FF4+, and a 4+ save along with the special rule Walker.
They also have some respectable weaponry packing either a Missile Launcher (45cm, AP5+/AT6+) and a Twin Linked Lascannon (45cm AT4+) OR a Power Fist (+1 MW CC attack) and an Assault Cannon (30cm, AP5+/AT5+).
These stats, for me, tend to lend themselves to one particular role – that of adding extra firepower and survivability to a drop-podding Devastator formation. Adding two Dreadnoughts to a Devastator formation with a Librarian comes to 400pts, which isnt bad for a Marine formation. It gives you additional firepower, especially AT firepower if you go with the ML/LC dreadnought, and it gives your Devastators the ability to claim a cover bonus from the AV Dreadnoughts. If there is cover nearby, then Walker allows you to safely dig in, while causing a real nuisance if you are near an objective. Combined with the fire from the Deathwind Drop Pods, this formation can cause a good amount of damage on the drop, and stick around long enough to really cause an issue.
The problem with using Dreadnoughts elsewhere in the list is that they tend to pose awkward issues with regard to transport. Marines as a list, because of their small size, need to have mobility and the ability to concentrate their forces effectively which requires their Rhinos. Dreadnoughts cannot keep up with formations in Rhinos, and although you could add them to a Tactical formation as an objective guard, this gets expensive very quickly. In addition, this leaves the Dreadnoughts as the only AV in the formation and easily snipe-able. The same is true of adding them to Terminators, or anywhere else in the army list.
So, dreadnoughts. Lovely models, awkward little buggers when it comes to list building!