Many armies, though not all, are built using a Combined Arms Detachment. It's a way of organising your forces to have a legal army. The Combined Arms detachment, as well as some other detachments, ask that it have certain unit choices selected, and those choices are based on the Battlefield Role of the unit. These are the Battlefield Roles: HQ (represented by a skull in the top corner of the dataslate) Troop (represented by a triangle in the top corner) Elite (represented by a cross) Fast Attack (lightning bolt) Heavy Support (explosion) Lord of War A Combined Arms detachment, for example, requires 1 HQ and 2 Troops, with an optional 1 HQ, 4 Troops, 3 Elites, 3 Fast Attack, 3 Heavy Supports, and 1 Lord of War in addition to this. Since Lucius and the Slanneshi Chaos Lord allow you to take Noise Marines as Troops rather than Elites, you can take more units of them than normal, and it'll free up your Elites slot for other things that you might want instead. Additionally, Troops in a Combined Arms Detachment have a bonus rule (Objective Secured) that they wouldn't get if they were an Elite in a Combined Arms Detachment. Combined Arms Detachments used to be the only way you could build an army, so this rule used to do a lot more than it does now. Nowadays there are many detachments that don't use these battlefield roles at all, meaning that it's not always necessary to pay attention to them. However, some things still will care about that battlefield role. Deathwatch, for example, have special rules depending on the Battlefield Role of the unit they're shooting at, and the unit will have that role no matter what army they're a part of.
|