cutting-in of a large searchlight may place such a load on the generator that the voltage will drop and the operation of the gyrocompass and other important instruments will be interfered with. When you are finished with the large searchlight, notify the Officer of the Deck so that he may inform the engine room again of the power change that is about to take place.

The front and rear doors of this light should never be opened before making sure that the drum is in the horizontal position with the elevation and train clamps and stowing locks secured. Under ordinary circumstances, the front and rear doors should be kept tightly closed during operation of the searchlight.

To operate the lamp, merely turn the main switch to the ON position. This will energize the carbon-arc elements as well as the ventilating fan, which will run continuously until turned off.

The elements used in the carbon-arc searchlight and the arc they produce are of prime importance. Every Signalman should thoroughly familiarize himself with the normal appearance of a properly burning arc. This information may readily be obtained in the instruction book for the equipment installed aboard your ship.

MAINTENANCE

After every extended run of the searchlight, and at least once each week for searchlights not in use, the interior of the drum and the lamp mechanism should be dusted and wiped clean. Particular attention must be given to rods, shafts, gears, contacts, and other closely fitted working parts of the mechanism which are dependent upon cleanliness for their free and proper function. Carbon dust and fragments of carbon must be blown or wiped out and a close inspection made to prevent jams and similar difficulties caused by deposits of dust forming a gum on points which are lubricated too liberally.

Each time the carbons are renewed, the front door glass, thermostat lens, and window should be wiped clean with clean, dry cheesecloth. At the same time clean all grease,

oil, dust, and moisture from the insulation and electriccontact surfaces.

Grease or oil should not be used on the heads. To keep them in good condition, apply a light coat of a kerosene and flake-graphite mixture once a week. This mixture should be used sparingly to prevent the excess from falling on the reflector.

After each 50 hours of operation of the arc searchlight, and not less than once each three months, the Electrician's Mate should remove the lamp from the drum, conduct a thorough cleaning, and check of all parts of the equipment.

YARDARM BLINKERS (NON-DIRECTIONAL)

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MULTI-PURPOSE LAMP

Figure 2-11.-Signaling equipment.

YARDARM BLINKERS

Yardarm blinkers, located near the ends of the yardarm, are made up of a cluster of several special nondirectional electric lamps protected from the weather. They are operated from a key on the signal bridge or other signal station. The light thrown by them goes out in ALL directions. See figure 2-11.

MULTIPURPOSE LIGHTS

The multipurpose light provides during darkness a method of visual communication that is directional and of limited range. This type of light obtains its electric power from batteries or from the ship's electrical supply lines. This incandescent lamp is flashed on and off by a trigger switch. The whole unit is portable and has its own carrying case for both the lamp and its batteries. See figure 2-11.

NANCY

We now come to a special application of flashing light which basically involves the same procedure as that for flashing light but requires special receiving apparatus. This system of visual communications is known as NANCY.

NANCY is a system of visual communications which uses a special light that is visible only with the aid of equipment designed for this purpose.

White light is actually a combination of light waves of many frequencies and colors which can be separated by using filters. Therefore, an ordinary electric light can be used to produce NANCY rays, and only NANCY rays, if all the visible light rays are filtered out. So, by covering any standard or specially constructed searchlight or beacon with a specially designed, opaque glass or plastic filter, you have an instrument which gives out only NANCY rays. These rays fall above the wave-length range of light which the human eye is capable of seeing, and just below the wavelength range of heat waves. NANCY rays are infrared waves and are therefore invisible to the unaided eye.

NANCY rays-like an ordinary searchlight beam-are

limited in distance to the horizon. The distance depends on the height of the light source and of the observer. The range of NANCY is reduced by adverse weather conditions to approximately the same extent as white light of comparable intensity. In conditions of very bad visibility it may be rendered virtually inoperative.

Equipment

During World War II the most widely used NANCY signaling gear was the type with a filter-lens and hood for mounting to the standard Navy 12-inch searchlight (fig. 2-12). With this gear attached, the light is operated in the same manner as an ordinary communication searchlight. Under average conditions it has an effective range of 10,000 to 15,000 yards, depending on the type of receiver used.

In addition to this equipment there are various other types of NANCY beacons which have been designed for recognition and reconnaissance as well as communication.

These include all-around lights of various design, beach markers, and course markers.

The infrared transmitting set, shown in figure 2-13, is presently installed aboard many ships of the Navy. The purpose of the equipment, as is that of the type H hood shown in figure 2-12, is to transmit signals by means of the infrared region of the frequency spectrum. The two transmitters may be operated as a steady source for "point of train" purposes, or they may be flashed in Morse Code for signaling or recognition. The beacons may be operated separately or simultaneously by either of two manual keys.

The beacons of the infrared transmitting set are designed to show a beam through 360 degrees in bearing and from 20 degrees below the horizontal to zenith in elevation. The radiated signals cannot be detected by the unaided eye at distances greater than 400 yards. The beacons do not show any white light; however, they are visible as dim red lights at short distances.