Atlas Recovery Tank
The Atlas Recovery Tank is the big brother of the Trojan no, not the one you're thinking of, you dirty /d/...anyways on topic, the Atlas is often used to tow back wrecked and destroyed Imperial vehicles, so that they can be salvaged and their machine spirits/armaments can be recycled. What? You're surprised that the Imperium contributes more to recycling than we do today? You will be surprised.
In order to tow the vehicles, the Atlas uses a powerful rear-mounted crane that is powerful enough to carry one Leman Russ, however, anything larger than it such as a Baneblade will require up to four Atlases to move. If a vehicle is completely destroyed beyond all hope of repair, it is stripped of usable equipment and unfired ammunition and its chassis left to rust over time.
The Atlas uses the same chassis as the Leman Russ Tank, but with the turret ring and armour plating removed, and the engine overcharged to provide more power. Being a recovery vehicle and thus situated at the back lines, the Atlas usually waits until the heat of battle has cooled enough and would proceed to tow back any destroyed vehicles. Due to this, they are lightly armed with only a hull-mounted Heavy Bolter for general protection, but as they share a Chassis with the Leman Russ they at least have good armor.
However, the Atlas can come equipped with Camo-Netting, Extra Armour, a Hunter-killer Missile Launcher, an Improved Communications System, a Mine Sweeper, a pintle-mounted Heavy Stubber/Storm Bolter, Rough Terrain Modifications, a Searchlight, Track Guards, and smoke launchers in order to improve viability much to the dismay of the Tech-Priests.
On the Tabletop
The Atlas is pretty much a giant Enginseer in the 8th Edition codex; it's an unarmed tank that repairs other vehicles. If nothing else, it's an interesting alternative. Oddly enough, it uses a Chimera statline instead of a Leman Russ statline.