Here's a piece of an article I'm working on for running a Traveller game wherein the characters are still in the Imperial Navy:
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STANDARD MATERIAL CONDITIONS: Conditions that affect the use of closures; such as hatches, airtight doors, watertight valves, flappers, etc., under normal operation.
MATERIAL CONDITION X-RAY - Fittings or marked with an 'X' must be closed. This condition is used only when grounded at a secure Downport, as it provides the least protection, and is set when the ship is in no danger of attack. A black X is placed on all fittings which must be closed at all times and when not in actual operation.
MATERIAL CONDITION YOKE - Closures marked 'X' and 'Y' must be kept closed. This is the normal underway material condition, and represents a minimal condition of airtight integrity; set and maintained while underway (including liftoff and landing) and in any port during wartime. For peacetime cruising, YOKE may be modified during regular working hours. A black Y is placed on all fittings which must be closed for wartime cruising conditions.
MATERIAL CONDITION ZEBRA - All fittings and closures marked 'X', 'Y', and 'Z' must be closed for maximum airtight integrity. "Set Condition Zebra" is the command to close all airlock doors, airtight hatches, and fittings throughout the ship. Usually follows the call to General Quarters; provides the maximum protection for ship and personnel for battle and emergency situations; such as fire, collision, or General Quarters; and is set when entering or leaving port during wartime. A red Z is placed on all fittings which must be closed for battle or emergency conditions.
SPECIAL MATERIAL CONDITIONS AND FITTINGS: Conditions that affect the use of closures, such as airtight hatches, watertight doors, valves, flappers, electrical and electronic equipment, etc., under abnormal operation.
WILLIAM - WILLIAM fittings are marked with a black W. These fittings are kept open during all material conditions. WILLIAM fittings are secured only as necessary to control damage or CBR contamination and to make repairs to the equipment served. You will find this classification on fire pumps and spaces that are manned during conditions XRAY, YOKE, and ZEBRA.
MATERIAL CONDITION CIRCLE WILLIAM - A material condition involving ventilation fittings and machinery marked with a 'W' inside a circle, which must be secured to control the spread of smoke in a fire, in preparation for an CBR attack, when at least one compartment will soon undergo a sudden decompression, when air pressure drops below a certain level, or when a compartment has undergone an unscheduled or explosive decompression.
CIRCLE WILLIAM - Vital valves that if secured would impair the mobility and fire protection of the ship. CIRCLE WILLIAM fittings are marked with a black W inside a black circle. These fittings are normally kept open, as is the case with WILLIAM fittings. They must, however, be secured to prevent the spread of damage and as a defense measure when a CBR attack is imminent. You will find this classification on doors and hatches to the Pilot House, Flag Bridge, and S
Signal Shelter (Radio Room).
CIRCLE X-RAY and CIRCLE YOKE are indicated by a black letter within a black circle. These classifications indicate that the fittings may be opened without special permission by personnel proceeding to battle stations or as required during routine security and inspection checks. The fittings must be secured immediately after use.
CIRCLE ZEBRA - Indicated by a red ‘Z’ within a red circle. This classification indicates that the fitting may be opened with permission from the Commanding Officer for health and comfort of the crew during prolonged periods of General Quarters (such as when distributing MRE's or during 'Comfort Breaks'). However, they must be guarded for immediate closure if necessary.
DOG ZEBRA - Indicated by a red Z inside a black D. These modified fittings are secured during condition ZEBRA and darken ship conditions. You must have proper authorization to open fittings with this classification when the ship is at either condition ZEBRA or darken ship. You will find this classification on all openings to the external hull, such as airlocks and portholes, excluding those classified XRAY or YOKE that do not have a darken ship switch or a darken ship curtain. DOG ZEBRA fittings are also secured when rigging the ship for SILENT RUNNING.
SILENT RUNNING - Occurs when the ship must remain undetected. During this condition, DOG ZEBRA fittings are secured, all non-essential systems are shut down, and essential systems are run at the minimum necessary to maintain the lives of the crew. Systems to shut down include: Propulsion (the ship coasts under its own momentum), active radar, transmitters, external lighting, IFF beacons, personal electronic devices, and anything else that may reveal the ship to hostile forces. Systems to reduce to minimum include life support, lighting, and artificial gravity. Personnel movement is also kept at a minimum, except to allow passage of written messages, for necessary bodily functions, or to maintain or repair essential ship’s equipment. MRE’s are issued after 24 hours of SILENT RUNNING.
RUNNING FLATLINE - Occurs when the threat of psionic detection is imminent. “SILENT RUNNING FLATLINE” is called, and special precautions are undertaken to reduce the risk of psionic detection, such as issuance of psionic shields, confinement of personnel to a psionically-shielded compartment, activation of a ship-wide psionic shield, or mandatory sedation of all non-essential personnel.
