Double Attack, known in Fire Emblem Fates and later games as follow-up attacks, is an action performed by characters in battle if their Attack Speed is sufficiently higher than the enemy's. After both the player and enemy have exchanged blows, if the character can double attack, they will perform a second attack afterwards. It is not to be confused with a Continued Attack caused by the Adept skill or a Brave weapon.
In most games up to Fire Emblem: New Mystery of the Emblem, double attacks occur when the attacker has an attack speed of at least 4 more than his opponent.
In Fire Emblem Gaiden and Fire Emblem: Genealogy of the Holy War, double attacks occur when the attacker has higher attack speed than his opponent. In Genealogy of the Holy War, characters must possess the Pursuit skill to be able to double attack.
In Fire Emblem: Mystery of the Emblem, double attacks occur when the attacker has an attack speed of at least 3 more than his opponent
In Fire Emblem Awakening and Fire Emblem Fates, double attacks occur when the attacker has at least 5 points more speed than his opponent.
In Fire Emblem Fates, certain weapons can affect double attack thresholds. For example, Steel weapons make it harder to perform a double attack (requiring 8 more speed), Effie's Lance makes it easier for the enemy to perform double attack (requiring equal speed) and so on. In certain circumstances it is even possible for both characters to perform double attack at the same time (for example if a character uses a Chakram to attack an enemy with equal speed).