The MP5SD3 is the classic Counter-Terrorist operation SMG, including the integral suppressor. The MP5SD3 is the 2nd quietest weapon in the game after the Veterinary Pistol this is because of the Subsonic 9x19 mm. The fire rate mixed with the silence of this weapon can be extremely helpful in certain hostage execution scenarios or moving troopers into a more advantageous position before executing a plan.