The Beretta M9 returns from ArmA: Armed Assault, and it is the standard sidearm of the USMC faction, typically carried by squad leaders and officers. A suppressed version of the M9 is available, and used mainly by members of the Force Recon unit 'Razor' team.
The Colt M1911A1 is the standard sidearm of USMC Force Recon units and snipers. The M1911A1 is also incorrectly depicted as the main sidearm of British soldiers in the Reinforcements expansion, substituting for the L9A1 pistol.
The Glock 17 is a weapon introduced in the Operation Arrowhead expansion, and is the standard sidearm of the Czech Army and also, erroneously though, German Kommando Spezialkr?fte (KSK) units; the real life German KSK units use the HK P8 as their standard sidearm. The in-game model features OD Green frame and a Glock tactical light.
Both the Makarov PM and its 6P9 PB suppressed version, returns from ArmA: Armed Assault. While the Makarov PM is the standard sidearm for most of the eastern factions involved in the game, including the Russian Army soldiers, CDF soldiers, ChDKZ rebels and NAPA insurgents, the 6P9 PB is used mainly by Russian Spetsnaz operatives.
The Taurus Tracker Model 455 is a weapon introduced in the Operation Arrowhead expansion, and simply referred to as the "Revolver" in-game. The Model 455 is used by Takistani military officers, and is also available in a gold-plated version.