The Mars-class Battlecruiser is an older STC-pattern that is currently out of favor with the Lord Admirals at Cypra Mundi, but remains an important part of Battlefleet Calixis. With few exceptions the Mars is the most potent warship available to a Calixian fleet commander. Most are assigned to a battleship division (two Mars-class vessels) stationed at key defensive points throughout the sector, ready to respond to major threats (in practice the Mars vessels spend most of their time at anchor, being too valuable to waste on patrols and minor incursions).

The Mars is a flexible design that, much like the smaller Lunar, is capable of dealing with virtually any combat scenario. The Mars, however, has a much heavier weapons loadout than the Lunar - including powerful batteries, multiple launch bays, lances, and a spinal-mounted weapon (the so-called 'Nova Cannon'). The combination of attack squadrons and spinal mount give the Mars excellent standoff range. The Mars is somewhat weak on the defensive and it's speed is also mediocre at best. It also lacks the definite kill capacity of more modern battleship designs at medium-short ranges.