The P08's silenced variant. Germany were developing silencers for their weapons, and tested them in secret night-time operations in the War. Only a few of these silencers were made, so silenced German weapons are mistical. In the game the P08S arrives with the Sabre Squadron mission pack, so this pistol can only be encountered on the new maps (Only in Multiplayer.).
Parabellum P08 (Luger) on Wikipedia