Some promoted classes, notably the Swordmaster and Berserker, have a Class Critical Bonus. This means that the class it applies to will always have a given chance for a critical hit, ignoring their Skill, Supports, and weapon factors.
The bonus first appeared in Fire Emblem: Fūin no Tsurugi, where Berserkers and Swordmasters receive a 30% chance of critical to what they would normally have. In the following games, this bonus was reduced to 15%. In Fire Emblem: The Sacred Stones, Amelia has this type of bonus, but only you promote her into a 3rd Tier Recruit.
Fire Emblem: Path of Radiance removed this bonus in the Japanese version, but it was restored in the American version, possessed by Swordmasters, Berserkers and Snipers. In Fire Emblem: Radiant Dawn, there were five levels of Class Critical Bonuses (Crit +5, Crit +10, Crit +15, Crit +20, Crit +25), represented as Skills permanently attached to the Sniper, Marksman, Reaver, Halberdier, Sentinel, Whisper, Assassin, Myrmidon, Swordmaster and Trueblade classes.
In Fire Emblem: Shadow Dragon, Berserkers and Snipers receive a 10% and 5% bonus respectively.