The kindred loyalists are the natural allies of the First Legion — a successor Chapter of the Unforgiven, a loyal Astartes force, or any zealous Imperial detachment that keeps the same wars. While the alliance stands, the Dark Angels and their kindred observe a map-level non-aggression and may lend one favour to each other in each post-battle sequence, and both gain a small reputation bonus for a campaign won together. But the Dark Angels tell the kindred nothing of the Hunt for the Fallen, and share no salvage taken from a Hunt battle — not even with an ally. Some secrets are kept from friends most of all.
Codex · Space Marines
Alliances2
Whothe kindred loyalists of the Imperium (a successor Chapter of the Unforgiven, a loyal allied Astartes force, or any zealous Imperial detachment that keeps the same wars as the First Legion)
Termscampaign-level alliance: while it stands, the Dark Angels and their kindred observe a map-level non-aggression and may lend one favour to each other per post-battle sequence; both gain a small reputation bonus for a campaign won together - but the Dark Angels tell the kindred nothing of the Hunt for the Fallen, and share no salvage taken from a Hunt battle even with an ally
Whoa fast, concentrated force that overwhelms one wing at a time (any highly mobile or hard-hitting gang built to fall on half the First Legion and break it before the other half converges - the Dark Angels' natural predator)
Termscampaign-level feud: while it stands, the Dark Angels gain bonus reputation for a decisive win where both wings converged intact, but the enemy gains reputation for every battle in which they broke one wing while the other stood apart; the feud runs until one side is driven off the contested world
The natural predator of the First Legion is a fast, concentrated force — any highly mobile or hard-hitting gang built to fall on half the strike force and break it before the other half can converge. While the feud stands, the Dark Angels gain bonus reputation for a decisive win in which both wings converged intact, while the enemy gains reputation for every battle in which it broke one wing while the other stood apart. It runs until one side is driven from the contested world. Call it a running argument, fought in blood, over whether the two wings are a strength or a fault line.