Chain-brothers While a Model with this Special Rule is within Unit Coherency of the other Model from your Army with this Special Rule, that Model gains a bonus of +1 to Hit Tests made in the Assault Phase. If a Model that is engaged in a Challenge is in the same Combat as the other Model from your Army with this Special Rule, that Model is treated as being in Unit Coherency with that other Model for the purposes of this Special Rule.
Chain-bonded This Prime Advantage can only be selected once per Army. When this Prime Advantage is selected, the Controlling Player must select another Unit which only includes Models with the World Eaters Trait that has the Command Battlefield Role from their Army. One Model in the selected Unit and one Model in the Unit selected to fill a Prime Force Organisation Slot with this Prime Advantage both gain the Chain-brothers Special Rule.