Material Conditions (NWP 3-20.31) establish the fighting integrity of the ship and maintain its survivability. The determination of the material condition set at any time is the responsibility of the Commanding Officer, who may authorize modifications of any material condition.
- X-Ray provides the least tightness and the greatest ease of access throughout the ship. It is set when the threat to the ship is minimal, during working hours when in port, or when there is no danger of attack or bad weather.
- Yoke is set when at sea, or in port during wartime.
- Zebra provides the greatest degree of subdivision and tightness to the ship. It is set immediately and automatically when general quarters is sounded. It is also set when entering or leaving port during wartime, to localize damage and control fire and flooding, or at any time the Commanding Officer deems it necessary. Modified Material Condition ZEBRA - allows movement around the ship for special conditions such as: Underway Replenishment (UNREP); Vertical Replenishment (VERTREP); Air Operations; Amphibious Operations; transit of known or suspected hazardous navigation areas.
One of the most important features of ship survivability is the ability to configure the ship to simultaneously allow the survivability system to function and the ship to be operated. Standard configurations representing varying degrees of closure and known as "material conditions" set the ship according to the degree of threat to the ship and the current operational directives. All fittings in the ship are marked to indicate how they are to be set during various material conditions. The determination of the material condition set at any time is the responsibility of the CO, who may authorize modification of any material condition. Closures are defined as closable openings in overheads, decks and bulkheads for access by personnel. Fittings are covers, valves, caps and plugs for access other than for personnel and for control of fluid flow. They may be on or in piping and ventilation systems, or in overheads, decks and bulkheads. For brevity, where context allows, the term fitting is used to include the meaning of both fitting and closure, and the term compartmentation is used to include both structural and fluid system segregation.
Condition XRAY provides the least watertight integrity and the greatest ease of access throughout the ship. It is set when the threat to the ship is minimal. Condition XRAY is set during working hours when the ship is in port and there is no danger of attack or from weather. The minimum degree of tightness permitted on an operational ship is condition XRAY. When condition XRAY is set, all fittings marked with a black X are closed.
Condition YOKE provides a greater degree of watertight integrity than condition XRAY, but to a lesser degree than the maximum condition. YOKE is normally set at sea and in port during wartime. When Condition Yoke is set, all fittings marked with black Xs and Ys, Circle X and Circle Y are closed. A modified condition YOKE is sometimes used at sea when cruising independently in good weather and calm seas and in port in peacetime. In the modified condition, YOKE fittings above the waterline are left open to improve ventilation and habitability. All other XRAY and YOKE fittings are closed.
Condition ZEBRA provides the greatest degree of subdivision and water-tight integrity to the ship. It is the maximum state of readiness for the ship's survivability system. Condition ZEBRA is set: Immediately and automatically when general quarters is sounded; When entering or leaving port in wartime; To localize damage and control fire and flooding when the crew is not at general quarters; and At any time the CO deems the maximum condition of survivability should be set. When condition ZEBRA is set, all fittings marked with black Xs and Ys, Circle X, Circle Y, Circle Z, red Zs and DOG Zs are closed.
There may arise certain situations during which the CO may wish to set a modified material condition ZEBRA. Setting of modified material condition ZEBRA will give a higher survivability stance than condition YOKE. At the same time, modified ZEBRA is less restrictive and will more readily allow the accomplishment of certain operational requirements. Modified ZEBRA may result as an upgrade from condition YOKE or as a downgrade from condition ZEBRA. Some of the situations that may make a modified material condition ZEBRA desirable are: Underway replenishment; Vertical replenishment; Air operations; Amphibious operations; or Transit of known or suspected hazardous navigation areas.
On larger ships, setting material condition ZEBRA in part or in total without all hands at general quarters will impede the ship's company from quickly manning battle stations. This situation could result in ZEBRA being set slower than had the ship been at material condition YOKE before the emergency. Large ships should therefore consider this when changing material condition.
Some fittings that are required to be open or closed for specific purposes carry special markings. Circle XRAY and YOKE fittings are access fittings to battle stations and compartments containing equipment that requires periodic checks or fittings that must be opened for ammunition transfer, as well as some systems. Circle XRAY and YOKE fittings are normally closed when conditions XRAY or YOKE are set. They may be opened without special authority when going to or securing from general quarters, transferring ammunition, periodic space or equipment checks or operating damage control equipment. Circle XRAY and YOKE fittings are marked with a black X or Y in a black circle.
Circle ZEBRA fittings are closed when condition ZEBRA is set. They may be opened with the permission of the CO during extended periods of general quarters for the preparation and distribution of battle messing, to provide access to limited sanitary facilities, to ventilate battle stations, to transit from squadron ready rooms to the flight deck and to allow limited access throughout the ship. Open Circle ZEBRA fittings must be guarded so they can be closed immediately. Circle ZEBRA fittings are marked with a red Z in a red circle.
DOG ZEBRA fittings are secured when condition ZEBRA is set and whenever the ship is darkened, regardless of the material condition that is set. During Darken Ship they are closed to prevent light inside the ship from showing outside. DOG ZEBRA fittings are marked with a red Z in a black D.
WILLIAM fittings are vital sea suctions, CPS zone ventilation fittings valves (serving vital equipment in manned spaces) and valves that must be open to maintain mobility and fire protection. WILLIAM fittings are open during all material conditions. They are secured only to control damage, contamination or to repair equipment served. WILLIAM fittings are marked with a black W.
Circle WILLIAM fittings, like WILLIAM fittings, are normally open, but are secured for protection in attack. Circle WILLIAM fittings are marked with a black W in a black circle.
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