40 CARROTWhat is unit coherency in Warhammer 40K?
Coherency is the spacing rule that keeps a unit fighting as one group. In 11th Edition a unit must satisfy three things at once: every model within 2" of at least one other model in the unit, the unit forming one linked group (no clumps separated by more than 2"), and every model within 9" of every other model in the unit.
What are the three coherency requirements?
First, the local rule: each model needs at least one other model of its unit within 2 inches — no model may drift off alone. Second, the connectedness rule: the unit must be one linked chain. Two internally-tight clumps separated by more than 2" are illegal even though every model in each clump has a neighbor; the unit has effectively split in two. Third, the envelope rule: every model must stay within 9 inches of every other model in the unit, which caps how far a legal chain can string out. Together the three rules mean a unit can spread to cover ground — wrapping an objective, screening a deployment zone — but only so far before it stops being one unit and starts being an illegal formation.
Why does coherency matter tactically?
Because the temptation is always to stretch. A ten-model squad strung to its limits can touch two objectives, block a charge lane, and screen a character all at once — but every inch of stretch is an inch closer to breaking one of the three rules when casualties come off. Practicing that trade-off is awkward on a physical table, where checking 9" between every pair of models is tedious. On 40 Carrot's true-scale virtual tabletop the app warns you when a unit breaks up, so you can push spacing to the legal edge, see exactly when it fails, and build the intuition before it costs you models in a real game.