“ The standard issue pistol of the U.S. Army.- In-Game Description ”
The M9 can be found in a freight yard in the Villa Verde province.
The Beretta starts with a standard issue 15-round magazine, and can be modified to accept 25-round extended magazines, various tactical laser sights, and a detachable suppressor. A unique M9 called "El General" is awarded to the player when they capture General Baro, a UNIDAD general. It sports a black paintjob with brown grips.
The weapon is also the default sidearm of Nomad, who will always draw a black M9 in cutscenes, regardless of the player's currently-equipped sidearm which, amusingly, will still appear inside its holster on his/her leg even in cutscenes. Holt, Midas and Weaver also have M9s as their default sidearms but they never use them. Karen Bowman, the Ghosts' CIA contact, also uses an M9 handgun during several cutscenes.
Random sicarios, and La Cabra, will also brandish two M9 handguns during random, out-of-combat interactions with certain NPCs, although they never actually use the weapon and will revert to their primary weapons if engaged in combat.