Overwatch (EU2012)

A soldier or alien with a remaining action can enter Overwatch (default hotkey Y). This ends the soldier's turn, but allows them to shoot at the first enemy that moves without any cover within their vision range during the enemy turn, albeit at a Aim penalty and without dealing critical hits. Firing on Overwatch at Dashing units also increases the Aim penalty.

The Penalty is a 0.7 modifier for Aim for any shots. The reduced chance to hit is further reduced again to 0.5 if the target is dashing. E.g., a soldier with 100 Aim has a 70% Chance to Hit on Overwatch, further reduced to 50% with a dashing target.

Some class abilities alter or improve various aspects and properties of Overwatch. These include Close Combat Specialist (Assault), Rapid Reaction (Heavy), Squadsight (Sniper), Opportunist (Sniper), Covering Fire (Support), and Sentinel (Support). While using Suppression the unit will also be given an Overwatch shot if the target tries to move.

Purposes

Overwatch can serve two tactical purposes:

• To keep an enemy unit pinned down or risk a reaction shot
  • To keep them from occupying key positions that allow them to flank your own units or better firing positions.
• To ambush unseen enemy units as they walk into the soldier's field of vision
  • To cover chokepoints such as corridors and flanks.
  • To shoot at just-activated alien packs before they reach cover after opening doors or stepping (with another unit) into their line of sight.

Overwatch and Reaction Fire

The differences between Overwatch and the Reaction Fire mechanic from the older games are:

• A unit must be specifically ordered to enter Overwatch every turn you want it used - simply leaving units with spare actions when ending turn will not allow them to fire on enemies (the only exception being when an enemy moves within the four-tile range needed to trigger a Close Combat Specialist Assault, who will then fire even if his weapon is empty). Reaction Fire, on the other hand, can only be prevented by draining a unit of Time Units, moving it where it can't see enemies off-turn, or by specifically disarming it.
• Overwatch is only triggered by enemy movement, not attacks, unless the overwatcher is a Support with the Covering Fire ability. On Reaction Fire the unit would fire at all sorts of actions (firing, moving, kneeling, etc.)
• Overwatch will only fire once, regardless of how many actions the unit still had left and it needs to be specifically activated. On Reaction Fire unit could automatically fire as many shots as long as they had Time Units left. On Overwatch it is required for the soldier to have any of these abilities to be able to fire more than one shot: Sentinel (Support class), Rapid Reaction (Heavy) or Close Combat Specialist (Assault).
• Overwatch, when active, will always fire the very moment an enemy moves into a valid position to fire at. Reaction Fire, on the other hand, may not occur if the moving unit has higher TU and/or Reactions figures (keeping in mind Time Units were reduced with every tile travelled). It also allowed most forms of movement to be made safely behind a guarding unit so long as he wasn't facing in the required direction to see it.
• All available units on Overwatch will fire on an enemy the moment they see it - at once. This is only time in the game multiple units may perform simultaneous attacks. Reaction Fire may only be performed by one unit at a time, meaning multiple shots are never "wasted" on units who only need one to go down.

• NOTE that a unit moving to a square that an enemy unit on Overwatch can see, will NOT trigger a shot if it's the last square of movement. This means you can, and aliens frequently will, sneak up to a corner, not trigger Overwatch fire, and proceed to murder with extreme prejudice. Less frequently, you can jump up, climb up, or drop down, and then stop and shoot, as long as the square being moved to is the last square of movement, and the only square in line of sight of the Overwatching unit.

Tips

• NOTE that the only way to take an alien out of Overwatch is to kill it or suppress it. Blowing them up or shooting them does not remove Overwatch.
• Moving into an Overwatching unit's line of sight doesn't trigger a shot unless you continue moving. Stepping up to a corner of a building, for example, will allow you to see what's around it without drawing fire - be wary of laying Overwatch traps for enemies on such spots, as they'll instead use it as an excuse to take a free flanking shot on you.
• When Overwatching be aware of what accuracy percentage you are likely to get. It is better to hunker down and double your defense bonus rather than risk missing with a 20% shot. Especially early on, when fielding rookies with low accuracy and weak weapons, it isn't worth the risk.
• The Opportunist perk turns a Squad Sight Sniper into one of the deadliest units in the game by removing the Aim penalty and allowing for critical hits, and is also a great lookout for stopping enemy thrusts with one shot.
  • Overwatch is probably a good idea if your Squadsight Sniper can't draw line of sight to an enemy, but has been otherwise attacking with Squadsight. Since the enemies can't see the Sniper, and thus won't know that you've activated Overwatch, there's a much better chance of the Overwatch triggering.
    • However, in Enemy Within, a sniper triggering Overwatch through Squadsight can no longer score critical hits, making this somewhat less useful.
• Close Combat Specialist gives as many shots as enemies step into less than four squares of the Assault. This ability also gives Overwatch shots during your turn so it can be used by shooting at Beserkers (who get to take an instant, free non-attack move upon taking damage) and lead them in the direction of a unit with the perk.
• The most efficient way to deploy a wall of Overwatch shooters is to place them staggered so that they'll fire separately at the alien rather than all of them spotting it and shooting at the same time. This also allows them to fire at different aliens rather than only engaging one out of a set of multiple attackers. However, in some situations it may be more worthwhile to focus all shots at the same time to drop better-armored targets (such as Sectopods).
• Due to the aim penalty, Overwatch can be more effectively used to "pin down" aliens while your squad manoeuvres, rather than for direct damage. An aliens will never (or very rarely) move if it sees an agent enter Overwatch (this holds true for aliens under suppressing fire as well). This can be exploited to great effect: it allows you to move your agents into flanking positions, while at the same time preventing the aliens from doing the same to you. Please note that aliens that do NOT see the agent go into Overwatch will still freely move, and will more than likely trigger a reaction shot. If all your squad's reaction shots are triggered, then the aliens will once again move freely, so care must be taken when setting them up for this tactic.
• On PC versions, there is a manipulatable bug with Overwatch, that can be of particular use to Squadsight (ie; Not-Snapshot) Snipers (or any trooper with an empty primary weapon) that involves going into Overwatch while the soldier is holding their pistol weapon. To trigger the bug, either manually reselect the Overwatching soldier and switch their weapon back to the primary, or use the hotkey to command that soldier into overwatch, and quickly click on the primary weapon icon in the bottom left corner before the camera moves on.
• In vanilla Enemy Unknown, there is an AI glitch for aliens: if they see two or more in-cover soldiers, at least one is flanking them, and they see either one go into overwatch, their AI locks up and they'll skip their next action. This is an excellent method to close in for a stun, or to bring a lower-level soldier around to score a kill for XP.
  • This is 'fixed' in Enemy Within: aliens and EXALT agents will most often move and risk non-Crit Overwatch damage rather than take flanking Crit shots.