Subterranean Assault Before the start of the first turn, when placing units into Reserve, a player must assign all units with the Subterranean Assault special rule and any Infantry units Embarked upon them to perform a Subterranean Assault. All models in a unit assigned to a Subterranean Assault must have the Subterranean Assault special rule, or be Embarked on a model with the Transport Subtype that has the Subterranean Assault special rule itself.
When rolling for Reserves, roll a single dice for all of the units assigned to the Subterranean Assault rather than rolling separately for each unit. If the roll is successful and the controlling player chooses to bring them into play then all of the Subterranean Assault units must enter play in that turn and follow this procedure:
Performing a Subterranean Assault
Once a Reserves roll for the units assigned to the Subterranean Assault has succeeded and the units are to be brought into play, the controlling player selects a single unit to deploy first. That player must place a single model with the Subterranean Assault special rule that is either a Dedicated Transport or a unit of its own (this model may have a unit Embarked within) anywhere on the battlefield that is at least 1" from any enemy model, battlefield edge or piece of Impassable Terrain and then scatter that model (see the Scatter rules on page 152 of the Horus Heresy: Age of Darkness rulebook).
If the model’s final position is within 1" of an enemy model, any battlefield edge or a piece of Impassable Terrain, the controlling player’s opponent may move that model to any position within 18" that is more than 1" from any enemy model, battlefield edge or piece of Impassable Terrain.
If there is no suitable position within 18" then the model may be repositioned anywhere on the battlefield that is more than 1" from any enemy model, battlefield edge or piece of Impassable Terrain.
Once this first unit has been deployed, roll a dice. On the roll of a ‘1’ the Subterranean Assault is Disordered, and the opposing player may deploy each remaining unit in the Subterranean Assault anywhere within 12" of the first unit without scattering, though no model may be within 1" of an enemy model or within Impassable Terrain. If the roll is a ‘2’ or higher, the controlling player deploys each other unit anywhere within 12" of the first, though no model may be within 1" of an enemy model or within Impassable Terrain. Any models Embarked on a model with the Transport Sub-type must remain Embarked and may not Disembark as part of a Subterranean Assault (but may Disembark normally during the following Movement phase).
Once all units are deployed, any enemy units with one or more models within 6" of any unit deployed as part of the Subterranean Assault suffer D6+3 Str 6, AP 4 Hits (Wounds caused by these Hits do not cause Morale checks or Pinning tests). Once all Hits are resolved, any enemy units that are neither Pinned or Falling Back and are within line of sight may choose to make the Interceptor Reaction (see page 309 of the Horus Heresy: Age of Darkness rulebook) targeting any one of the units deployed as part of the Subterranean Assault. Note that no Reaction other than Interceptor may be made against the deployment of a unit as part of a Subterranean Assault.
Once all units from the Subterranean Assault have been deployed and any Interceptor Reactions have been resolved, the turn proceeds as normal. Units that have been deployed as part of a Subterranean Assault may Move, Run or Shoot as normal. However, only units deployed aboard a model with the Transport Sub-type with the Assault Vehicle special rule may declare and resolve a Charge and Assault as normal. Other units deployed as part of a Subterranean Assault may not declare or resolve a Charge on the same turn as they are deployed.
