Shooting with war engines
When you reach the "Shoot with war engines" step in the turn sequence then it is time to shoot with your War Engine units. This is usually a moment of high drama and excitement — will your carefully positioned behemoths live up to their fearsome reputations and lay waste to the enemy?
War engines make excellent mobile weapons platforms — but their sheer mass means that they can’t point their weapons in any direction at a moment’s notice. The rules here add some extra detail to reflect these features.
Each War Engine unit has one or more weapon mounts. 
These are simply the weapon-carrying locations on the war engine, and have names like Left Carapace or Right Arm. Each weapon mount also has:
A weapon system that defines the weapon effects that exist in this mount (Weapon systems).
A weapon arc that restricts the line of fire of the weapon system (Weapon arcs).
We list each weapon mount that a War Engine has in a separate line on the unit’s data sheet, along with the corresponding weapon system details and weapon arc.
Types of weapon system
Each weapon system provides one of these weapon combinations: 
One or more shots from a ranged super-heavy weapon. Multiple shots from such a weapon system are just like multiples of that super-heavy weapon, except that we treat the weapon system like a single super-heavy weapon for various game effects.
A close combat super-heavy weapon, such as Close Combat Weapons or Ripper Tentacles. In some cases the weapon system may combine this with a basic Firepower value.
A basic Firepower value. This represents some kind of battery of heavy weapons.
Where you can choose from a wide range of weapon systems, we leave empty boxes on the data sheet for you to fill with the information to match your particular choices.
Game effects of weapon systems
While you may split fire to target different detachments with different weapon systems, you may not split fire with the effects of a single weapon system.
For critical damage results, apply effects that destroy or restrict a weapon to the whole weapon system. [TODO: If we reference 'weapon system' rather than 'weapon' on every data sheet in future, perhaps we can do away with this bullet point?]
Where a weapon system does not have a basic Firepower value, treat it like a single super-heavy weapon:
When your detachment’s Firepower is halved for any reason, roll to lock on with each of its super-heavy weapon systems — not with each individual shot.
Super-heavy weapon systems may contribute to the placement of Blast markers in one of two main ways, depending on whether or not they contribute Firepower in the attack.
After Firepower, each remaining Blast marker suppresses one entire super-heavy weapon system.
In a firefight, a super-heavy weapon system contributes 1 Firepower — regardless of the number of shots.
Each weapon mount on a War Engine unit has a weapon arc. 
The arc constrains the line of fire for the weapon system in that mount. You may only use weapons in that weapon system to target detachments that are inside within that arc, and you may only allocate hits to units that are inside of that arc.
We use icons on the War Engine data sheets to show what arc applies to each weapon mount.
The arrow in the centre of each icon represents the facing of the war engine. The black segment indicates the weapon arc, relative to the facing.
From top-left to bottom-right, these icons represent:
Front-left 180°; Front 90°; Front 180°; Front-right 180°
Left 180°; All Around (360°); Rear 180°; Right 180°