There are three material conditions of readiness, which may be set on the ship: XRAY, YOKE, and ZEBRA. Material conditions of readiness refer to the degree of damage, which the ship is prepared to sustain and survive. In condition XRAY, no damage is expected and many fittings are open. In condition ZEBRA, the maximum degree of subdivision is maintained; each compartment is isolated with the exception of some vital items such as firemains, electrical circuits and ventilation. Condition YOKE is the normal setting. During the work day, YOKE MODIFIED is normally authorized. This means that certain YOKE fittings above the water line may remain open in order to increase ventilation and habitability on the ship. The following is a summary of the damage control classifications and their meanings: "X"- Remains closed at all times. Must get the OOD's or DCA's permission to open. Circle "X"- Remains closed at all times when not in use. May be opened without permission if it is guarded or if it is closed immediately after passing through. "Y"- Closed when YOKE is set, must obtain OOD's or DCA's permission to open when YOKE is set. Circle "Y"- Closed when YOKE is set. May be opened without permission if it is guarded or if it is closed immediately after passing through. "Z"- Closed when ZEBRA is set, normally for General Quarters and other emergencies: must get OOD's or DCA's permission to open. Circle "Z"- Closed when ZEBRA is set. May be opened with the Commanding Officer's permission during prolonged periods of general quarters. The opening of these fittings allows evolutions such as the preparation and distribution of battle rations, and ventilation of battle stations. When open they must be guarded. Dog "Z" -These modified fittings are secured during ZEBRA and darken ship conditions. You must have proper authorization to open these fittings. "W" -Normally open or running at all times except to isolate damage or contamination or to effect repairs to units served. Circle "W" Closed during Nuclear, Biological or Chemical (NBC) attack to prevent contamination of the interior of the ship. Could be more specific but this is the jist of it.

Thanks Sam that was very helpful. Jersey Devil