Editing Warhammer 40,000/9th Edition Tactics (section)

===Terrain 101===
New as of 9th, pieces of terrain will all have certain traits.

*'''Cover:''' {{W40kKeyword|Infantry}}, {{W40kKeyword|Beasts}}, and {{W40kKeyword|Swarm}} models receive the benefits of cover from an Obstacle while within 3″ of an obstacle unless, when you resolve an attack that targets said model's unit, you can draw straight lines, 1mm in thickness, to every part of a model's base from a single point on the attacking model’s base (or hull) without any of those lines passing over or through any part of the obstacle.  {{W40kKeyword|Infantry}}, {{W40kKeyword|Beasts}}, and {{W40kKeyword|Swarm}} models receive the benefits of cover from Area Terrain while within it.  Nothing else gains the benefits of cover from the core rules with the possible exception of Dense Cover, which is discussed in that entry below.
**'''Dense Cover:''' If this terrain feature is at least 3" in height, then subtract 1 from the hit roll when resolving an attack with a ranged weapon unless you can draw straight lines, 1mm in thickness, to every part of at least one model’s base (or hull) in the target unit from a single point on the attacking model's base (or hull) without any of those lines passing over or through any part of any terrain feature with this trait. Models that are on or within an Area Terrain feature with this trait do not suffer this penalty if the only terrain feature these lines pass over or through is the terrain feature that the attacking model is on or within. Models within 3" of an Obstacle terrain feature with this trait do not suffer this penalty if the only terrain feature these lines pass over or through is the terrain feature that the attacking model is within 3" of.  This penalty is also ignored when the target is either W18+ or {{W40kKeyword|Aircraft}}.
***The Core Rules FAQ contains "Designer's Notes" which contradict the Core Rules on Dense Cover, but ''does not'' actually errata the definitions of Obstacle, Area Terrain, or Dense Cover:
****''Also, in the same way that Obscuring terrain ‘blocks’ visibility when it is in between the firing model and its intended target, Dense Cover terrain imposes a hit penalty whenever it is between the firing model and its intended target (with the noted exceptions). '''It is not required for a unit to be fulfilling the criteria of ‘gaining the benefits of cover’, as described for Obstacles and Area Terrain, for this penalty to hit rolls to apply''' (but also note that any rule that ignores the benefits of cover, or that ignores the benefits of cover that impose a penalty on hit rolls, would still ignore that penalty).''
***As a result, you need to discuss with your opponent how to interpret this.  Common options are listed below:
****The Designer's Note changes the conditions for Dense Cover to those of Obscuring Terrain: use the conditions for Obscuring (changing the height requirement to 3") and nothing else.  This means units on or within Dense Cover gain no benefit (just as they do not for Obscuring), but units "behind" Dense Cover benefit unless Aircraft or W18+, even if not Infantry, Beast, or Swarm.
****The Designer's Note adds to the conditions for Dense Cover such that both rules apply at once: under the conditions of Obscuring (changing the height requirement to 3"), all non-Aircraft non-W18+ benefit, and while on or within Dense Cover, Infantry, Beasts, and Swarms benefit (provided they are neither Aircraft nor W18+).
****The Designer's Note is ambiguous, so without explanation, has to be ignored.  Treat this text as not existing, and like Light or Heavy cover, only Infantry, Beasts, and Swarms benefit.
**'''Heavy Cover:''' +1 to armour saves against attacks made with melee weapons unless the attacked model made a charge this turn.
***As a practical matter, ''all'' heavy cover is also light (and hence none of it is dense).
*'''Light Cover:''' +1 to armour saves against attacks made with ranged weapons.
**As a practical matter, light and dense cover are treated by GW as mutually exclusive, and heavy is treated as light but moreso (some light cover is also heavy and all heavy cover is also light).
*'''Obstacle:''' Terrain you can be on but not within.  Has a series of traits that can be added on which in practice amount to "levels" of Obstacle:
*#Baseline: Doesn't have Exposed Position, Unstable Position, or Defence Line.  No additional rules.
*#'''Exposed Position''':  This will ''never'' have Unstable Position or Defence Line.  A model does not receive the benefits of cover if it is standing on this terrain feature. If you are behind it you may, though.  Can't be on Area Terrain because you can be within Area Terrain but not on it.  Note that this means the terrain will also deny cover to a unit on it that has a special rule granting cover - Exposed Position removes cover benefits even if the Obstacle doesn't grant them.
*#'''Unstable Position''' without Defence Line:  This will ''never'' have Unstable Position.  You can't stand units on top of this thing. No exceptions. You can walk them over it or through it, but not on top of it.  Can't be on Area Terrain because you can be within Area Terrain but not on it.
*#'''Defence Line''':  This will ''always'' imply Unstable Position (and hence can't be Exposed Position).  If an enemy unit is within 1" of this terrain feature, you can still make a charge move against it so long as the charging unit ends its charge move touching that terrain feature and within 2" of the target unit. Units are eligible to fight, and models can make attacks with melee weapons, if their target is on the opposite side of this terrain feature and within 2".  Doesn't actually require Unstable Position RAW, but because UP is the only kind of terrain where you can need this rule in order to engage, in practice is only found on some UP.
*Movement-modifying traits.
**'''Breachable:'''  All {{W40kKeyword|Infantry}}, {{W40kKeyword|Beasts}}, and {{W40kKeyword|Swarm}}s can move through any walls, girders, chains, or foliage of this feature without impediment - nothing else can.  As a practical matter, this usually means the listed units can easily move horizontally through Breachable terrain, while everything else has to pay additional movement to go over it.
***For unclear reasons, in practice 100% of Breachable terrain is also Defensible.
**'''Scaleable:''' Only {{W40kKeyword|Infantry}}, {{W40kKeyword|Beasts}}, {{W40kKeyword|Swarm}}s, and {{W40Kkeyword|Fly}} can be set up or end a move on top of an Obstacle with this (for anything else, it's functionally Unstable Position).  Likewise, only the same set of models can be set up or end a move on the non-ground floors of an Area Terrain feature with this trait (other models can only be set up or end a move on the ground floor). Finally, the terrain is Breachable with respect to a different set of features than actual Breachable (basically, features that would usually block ''vertical'' movement):  {{W40kKeyword|Infantry}}, {{W40kKeyword|Beasts}}, and {{W40kKeyword|Swarm}}s can move through the floors, ceilings, and gantries of this terrain feature without impediment.
***This means you'll never see terrain which is both Scaleable and Unstable Position (and hence you'll also never see Scaleable and Defence Line), as that would cause a rules paradox.
**'''Difficult Ground:''' Or rather, Difficult Terrain. Reworked to not be as crippling, this now only robs 2" of normal/advance/fall back movement and applies -2 to charge rolls for any that cross over it unless the entire unit has {{W40Kkeyword|Fly}} or it has {{W40Kkeyword|Titanic}} ''and'' the feature is less than 3" tall.
***For whatever reason, in practice all difficult ground is area terrain, even though in principle you could have difficult obstacles.
*Durability-enhancing traits.
**'''Defensible:''' Non-engaged {{W40kKeyword|Infantry}} units wholly within this (if Area Terrain) or wholly within 3" of it (if Obstacle) that are charged (if an Obstacle, draw a line 1mm thick between the closest parts of the bases or hulls of the two closest models in the two units; if the line passes over/through the Obstacle, then Defensible applies, otherwise it does not) can either hit with their overwatch shots on a 5+ (which doesn't enable overwatch, it just increases your accuracy if you are overwatching) or be barred from overwatch but gain a +1 bonus to hit in the next Fight phase.
**'''Inspiring:''' Units within 6" of this terrain piece gain +1 to Leadership. This can be locked to certain faction keywords so you don't have guardsmen being inspired by being near a chaos shrine or necrons inspired by statues of imperial saints.
**'''Obscuring:''' For your tall terrain pieces. Anything taller than 5" will block LOS for units on either side of it. However, it does nothing if either unit (the observer or the observed) is inside or on it, or if the observed unit's an {{W40kKeyword|aircraft}} or is W18+.


In the table below, under "Category", "Exposed Position" means an Obstacle with Exposed Position (and hence neither Unstable Position nor Defence Line), "Unstable Position" means an Obstacle with Unstable Position and neither Exposed Position nor Defence Line, and "Defence Line" means an Obstacle with Unstable Position and Defence Line.  "Area Terrain" is Area Terrain that isn't Difficult Ground and "Difficult Ground" is Area Terrain that is.

Cover is "Dense", which means Dense but not Light or Heavy, "Light", which means Light but not Dense or Heavy, or "Heavy", which means both Heavy ''and'' Light.  "No" simply means no cover.

"Breachable" is "Breachable" if both Breachable and Defensible, "Defensible" if Defensible but not Breachable, and "No" if neither.

{| class="wikitable sortable" style="margin-left:auto;margin-right:auto;"
|+ Terrain Features
! scope=col | Name
! scope=col | Category
! scope=col | Breachable
! scope=col | Cover
! scope=col | Obscuring
! scope=col | Scaleable
! scope=col | Inspiring
|- style="text-align:center;"
! scope=row | Armoured Containers
| Exposed Position || No || {{font color|Light|green}} ({{font color|Exposed&nbsp;Position|red}}) || No || {{font color|Yes|green}} || No
|- style="text-align:center;"
! scope=row | Barricades and Fuel Pipes
| Defence Line || {{font color|Defensible|green}} || {{font color|Heavy|green}} ||colspan=3| No
|- style="text-align:center;"
! scope=row | Battlefield Debris 
| Exposed Position || No || No ({{font color|Exposed Position|red}}) ||colspan=3| No
|- style="text-align:center;"
! scope=row | Craters
| Difficult Ground || No || {{font color|Light|green}} ||colspan=3| No
|- style="text-align:center;"
! scope=row | Imperial Statuary
| Unstable Position || No || {{font color|Light|green}} ||colspan=2| No || {{font color|{{W40Kkeyword|Imperium}}|green}}
|- style="text-align:center;"
! scope=row | Industrial Structure
| Area Terrain || {{font color|Breachable|green}} || {{font color|Dense|green}} || No || {{font color|Yes|green}} || No
|- style="text-align:center;"
! scope=row | Ruined Walls
| Defence Line || {{font color|Breachable|green}} || {{font color|Dense|green}} ||colspan=3| No
|- style="text-align:center;"
! scope=row | Ruins
| Area Terrain || {{font color|Breachable|green}} || {{font color|Light|green}} ||colspan=2| {{font color|Yes|green}} || No
|- style="text-align:center;"
! scope=row | Woods
| Difficult Ground || {{font color|Breachable|green}}  || {{font color|Dense|green}} ||colspan=3| No
|}

====Tactical Deployment====
Added in the Tactical Deployment Chapter Approved Mission Pack, this system adds points costs to terrain and enables them to be deployed by each side as if they were units; the point limit for deploying terrain is proportional to the size of the game (e.g. 50-100 points for Combat Patrol and 300-400 for Onslaught). Terrain deployed in this way will gain Terrain Abilities in addition to the normal traits, which grants them more complex effects than usual.