Co-Op Attack or Team Attack is an ability of units in the Valkyria Chronicles series. It allows allied units in close proximity to one another to perform a synchronized attack when one of those units opens fire, effectively performing multiple actions for a single Command Point.
A Co-Op Attack is initiated when a soldier opens fire with a direct-fire weapon, with allied soldiers in close proximity to them and within range to hit the target with their own weapon. If the current attack will be a Co-Op Attack, boxes showing the name or names of those participating in the Co-Op Attack will appear in the top-right corner of in the interface. A Co-Op Attack also will not trigger if the target is outside the weapon range of the unit initiating it, even if their attack still deals damage.
Units who are listed as friends will deal extra damage when performing a Co-Op Attack, and also have special speech for joining a Co-Op Attack with one of their friends.
In Valkyria Chronicles, only infantry units that can perform Interception fire (ie Scouts, Shocktroopers and Engineers, and the Edelweiss and Shamrock with their coaxial machine guns) can participate in a Co-Op Attack. Lancers can initiate a Co-Op Attack if their target is close enough for the nearby units to hit it, but cannot participate in one initiated by another unit.
In this game the use of coordinated Co-Op Attacks with groups of Shocktroopers is instrumental in getting kills against infantry boss enemies within the A-rank turn limit on a first playthrough, specifically Selvaria Bles and Maximilian.
In Valkyria Chronicles 3, Co-op attacks receive a small versatility buff; if lancers and snipers are led around via Kurt's Direct Command ability, they too, can take part in co-op attacks without using ammo, allowing for their usable to be considerably increased.
In Valkyria Chronicles 4 the ability is greatly expanded: now Snipers, Lancers (with other Lancers, and not when using Mortar-Lances), and even Tanks will participate in Co-Op Attacks if they are positioned correctly. It is worth noting that this can be a problem, however, in that units with limited ammunition will expend it by participating in a Co-Op Attack: this is particularly an issue with Snipers. Units that are out of ammo cannot participate in Co-Op Attacks.
A tank that participates in a Co-Op Attack will use its main gun with any other tank with a main gun (Hafen, the DLC Edelweiss and Glory with its default turret) and Lancers vs enemy vehicles (but not structures), and its machine gun with Scouts, Engineers, Shocktroopers, and Sniper. Glory's alternate turrets are an oddity: the Gatling turret will have the Hafen fire its machine gun and fire if the Hafen is using its machine gun, while the flamethrower turret will only initiate a co-op attack if the machine gun is used. Tanks will never fire mortar rounds in a Co-Op Attack, and cannot Co-Op with a tank that is firing a mortar round.