Unlike the other types of attacks, Op Fire is announced and resolved during the opponent’s action turn. A unit in Op Fire mode may attack the active enemy unit immediately after the active unit moves into a hex within range and LOS of the Op Fire unit.
Note the following rules about Op Fire attacks:
- A unit may only engage in an Op Fire attack if the active enemy unit has just moved into a hex within range and LOS. If the active unit has not moved, it cannot be the target of an Op Fire attack, even if it is within range and LOS.
- If an enemy unit spends movement points for a purpose other than moving into a new hex (for example, using a special ability, or entering an entrenchment), this does not trigger Op Fire. instead exiting a fortification (including entrenchments) does trigger enemy Op Fire.
- The active unit can only be subject to one Op Fire attack for each hex that it moves into. Thus, if the opponent wishes to attack the active unit in a certain hex with more than one unit in Op Fire mode, he must use combined fire.
- If a unit is capable of firing multiple Op Fire attacks during a round (such as the machine gun crew, see page 37), it may only make one attack against a single enemy unit during that unit’s activation. Thus, it is not legal for a machine gun crew to engage in Op Fire (or participate in combined Op Fire) against the active unit in one hex, and then engage in Op Fire against the same active unit as it moves into an adjacent hex.
- If the Op Fire attacker decides to make a suppressive attack against an active unit, and manages to either pin or disrupt an active squad or damage an active vehicle, the active unit is immediately fatigued.
Exception: Being only lightly damaged by enemy Op Fire does not cause a heavy vehicle to become fatigued.
After resolving an Op Fire attack, the lead Op Fire unit, as well as any other Op Fire units that supported the attack with combined fire, are fatigued. Simply flip the activation token from its Op Fire side to the fatigued side. These units are no longer considered to be in Op Fire mode.
See detailed FAQs here: Op Fire.