The Code Cylinder is a quest item in Call of Duty: Black Ops III on the zombies map Gorod Krovi. It may refer to the Dragon Command Code Cylinder, Supply Depot Code Cylinder, Tank Factory Code Cylinder, or Master Code Cylinder.
The Dragon Command, Supply Depot and Tank Factory Code Cylinders are regular drops from zombies, only obtainable after turning on the power and speaking with Sophia. Only one may be held at a time. The Code Cylinders may be placed in the corresponding console at the relevant location, matching the color of the Cylinder. Upon inserting a Code Cylinder into its matching console, a Groph Pod will be called into the map and fall onto a random location, indicated by a distinct beam of light shooting into the sky, which must be defended from zombies that will prioritize attacking it over the player. The first time a Pod is called and successfully defended from each of the Cylinders, it will contain a piece of the Dragon Network Controller, which is required to reach the map's Pack-a-Punch Machine. Subsequent completions of any Groph Pod defenses for Cylinders that have already rewarded the player with its piece of the Dragon Controller Network will reward the player with a random, standard Power-Up.
Master Code Cylinder
The Master Code Cylinder is obtained as part of the Love and War Easter Egg. In order to do so, the player must kill a Valkyrie Drone near a tarp-covered generator in the basement of the Hatchery. After doing so, the player will have five minutes to both locate and draw the Cylinder through a series of pneumatic tubes which stretch across the map by adjusting the air flow on the pneumatic tube receptacles. Once obtained, the Master Code Cylinder can be entered into Sophia's console, prompting her to request a password to be entered on a series of rotating disks. The disks can be manipulated by shooting or knifing them, and entering password "KRONOS" will progress the Easter Egg.