Reaction Fire (UFOAI)

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Units can fire on enemy units when they wander into their field of view during the enemy's turn. Soldiers will execute a reaction shot when an enemy unit spends more TU in their field of view than the cost of their reaction fire.

Understanding Reaction Fire

While this mechanic is simple and straightforward, using it effectively can quickly become complex because of the range of actions and firemodes which affect how many TUs one unit will spend in front of another. If the enemy is able to spot your soldier, fire their weapon and then return to cover using fewer TUs than the cost of your soldier's Reaction Fire firemode, your soldier will not fire.

To illustrate this, let's consider an example in which a soldier has activated Reaction Fire. During the alien's turn, the alien appears from behind a wall, spots the soldier, fires on him and then moves back behind the wall. The following timelines show what will happen when the soldier or alien chooses different firemodes.

Soldier Doesn't Fire

Soldier Reaction Fire firemode = 12 TUs (Burst fire from Assault Rifle)

Alien firemode = 8 TUs (Snap Shot from Plasma Rifle)

1. Alien moves one grid from behind wall into view (2 TUs)
2. Alien chooses to fire (8 TUs)
3. Alien fires first because total TUs (2 + 8) are less than soldier's Reaction Fire (12 TUs).
4. Alien moves one grid back behind wall (2 TUs)
5. Alien has now spent 12 TUs, but is behind the wall and therefore out of view of the soldier. No reaction fire is taken.

Soldier Fires First

Soldier Reaction Fire firemode = 8 TUs (Snap Shot from Assault Rifle)

Alien firemode = 8 TUs (Snap Shot from Plasma Rifle)

1. Alien moves one grid from behind wall into view (2 TUs)
2. Alien chooses to fire (8 TUs)
3. Soldier fires first, because the alien has spent more than 8 TUs (snap shot) in view of the soldier.
4. Alien fires second.
5. Alien moves one grid back behind wall (2 TUs)

Soldier Fires Second

Soldier Reaction Fire firemode = 16 TUs (Auto fire from Assault Rifle)

Alien firemode = 8 TUs (Snap Shot from Plasma Rifle)

1. Alien moves three grids from behind wall into view (6 TUs)
2. Alien chooses to fire (8 TUs)
3. Alien fires first, because total TUs spent (14) is less than soldier's Reaction Fire cost (16 TUs)
4. Alien moves one grid back towards the wall (2 TUs)
5. Soldier fires after the alien has moved, because the alien has spent 16 TUs in view of the soldier.

As you can deduce from these examples, Reaction Fire is more effective when firemodes that use less TUs are selected. In order to ensure your soldiers will pre-empt enemy fire and shoot first, your soldiers must use a firemode that is quicker than the enemy's. It is also possible to execute Reaction Fire if the enemy does not fire, but spends too many TUs in view. Any TU spent in view of a soldier will add to the Reaction Fire counter, including crouching and turning in a new direction. But the alien AI is particularly good at popping up around corners, firing, and retreating to cover. You're only likely to get Reaction Fire on enemy movement at long distances, where the alien AI feels safer moving around.

For this reason, weapons traditionally thought of as good "overwatch" weapons, such as Sniper Rifles, are not effective when used in Reaction Fire. In UFO:AI, Reaction Fire is much more appropriate for defensive purposes and close-quarters situations where the player must win the "Reaction Fire Contest" and fire first.

How to use Reaction Fire effectively

In order to use Reaction Fire effectively, you must understand and prepare for the "Reaction Fire Contest". When opposing units spot each other, there is typically a race to fire first that is based on the number of TUs each unit will spend to fire their weapon. At close quarters, when shots are very likely to hit, winning this contest is especially important.

Because the active unit typically has to spend 2 TUs moving into view, the defensive unit often has a slight TU advantage. If your soldier spots an enemy during their movement and the enemy sees them, your soldier has already spent 2 TUs moving into view. If your soldier and the enemy both use 8 TU firemodes, the enemy will fire first because your soldier's total TU spent will be 10 TU.

Knowing the enemy's weaponry and the TU costs of their firemodes will go a long way in deducing which firemodes will be effective when used for Reaction Fire.

  • Plasma Pistol - At the start of the game, the aliens wield the Plasma Pistol, which costs 6 TU to fire. The only weapon that can beat this early in the game is the pistol.
  • Plasma Blaster, Plasma Rifle, Hovernet and Particle Beam Rifle - These weapons (and alien) cost 8-10 TU to fire their cheapest firemode. Shotguns, Plasma Blasters, Assault Rifles or Plasma Rifles are the most effective firearms to beat these weapons. However, none of these weapons are very effective at long range. When expecting long-range Reaction Fire, it may be safe to receive fire and use the more expensive burst modes of rifles.
  • Needler, Heavy Needler, Particle Beam Cannon - These weapons typically cost 12-13 TU to fire their cheapest firemode. Most effective Reaction Fire weapons will beat them to the draw.

When Reaction Fire won't fire

In some cases, Reaction Fire won't fire when you may expect it to. These include:

  • Out of range: All weapons have a maximum range. If the target exceeds this range, no Reaction Fire will be taken.
  • Lost view: If a target moves out of view, even very briefly, the Reaction Fire counter is reset to 0. TUs spent are not cumulative.
  • Not activated: Reaction Fire must be activated by selecting an appropriate firemode and clicking the Reaction Fire button to enable it. It's easy to forget, so don't forget!

Common misconceptions

Because Reaction Fire works differently in UFO:AI than it does in other X-Com games, it is often the source of many misconceptions.

  • Reaction Fire is always fair. Aliens are not better than soldiers at it and soldiers can not become more proficient at it. Reaction Fire can not be trained like in the original X-Com. Reaction Fire will always depend on TU costs for soldiers and aliens, and it can always be predicted by paying close attention to TUs spent and observed.
  • Reaction Fire is not a free shot. Soldiers who have activated Reaction Fire will not automatically get to fire first when an enemy appears. Reaction Fire is not Overwatch like in the new XCOM.
  • Reaction Fire is not overwatch. Reaction Fire is not effective in a real-world role of "overwatch". Snipers are terrible at Reaction Fire because of their high TU costs.
  • Reaction Fire is not automatic. Players need to click to activate Reaction Fire, or a soldier will not fire even if they see an enemy and it is within range.