What They Are

1. Pyrotechnics used by the United States Navy are modifications of fireworks displays used for signaling, marking, or illuminating objects in tactical operation.

Each display has an operational function indicated by its color, pattern, or effect.

Pyrotechnic equipment consists of various type of ammunition and the proper firing de-vice for each.

Some types of surface pyrotechnics are fired from pistols, from mortar type projectors, or are ejected from submerged submarines by means of compressed air. Other types can be launched by hand, while still others, when mounted on the bridge of a ship, are ignited by lanyard.

Effective

2. The effectiveness of pyrotechnics is generally dependent on three major fators: de-sign, position, and the amtospheric conditions prevailing at the time of use. Variations of design govern the candlepower of the flare or signal, the color prodruced by the charge, and the continuity of the burning pyrotechnic candle. The color and reflective charac-teristics of the objective often affect the visibility of pyrotechnics. Open ground, such as an airfield, will reflect three to four times as much light as will woods or deep water. Po-sition, distance, relative position, background, or the angle of observation also alter visi-bilty; while the degree of light or darkness, fog, haze, or other atmospheric conditions have self-evident effects.

Relation of Design to Visibility

3. Candlepower, length and continuity of burning, and color are given careful considera-tion in the design of pyrotechnics, as all three affect visibilty. Each item of ammunition contains a pyrotechnic candle, the design and chemical formula of which governs the candlepower (amount of light given off by a unit weight of candle) and the length and continuity of burning. A short, thick candle gives greater illumination for a shorter time than a long, thin candle of equal weight. The latter burns for a longer time but with less brilliance. Color plays an important part in the design of pyrotechnics, as the eye is most sensitive to colors in the middle spectrum. For example, reds and yellows have greater visibility through haze and fog than do other colors.

Relation of Position to Visibility

4. Another factor determining visibilty is the position of the pyrotechnic flare in relation to the objective and the observer. Light value varies in inverse proportion to the square of its distance from the objective. For example, a light placed one foot from an object illuminates that object four times as much as a light placed two feet from the same ob-ject. Excpet when the observer is temporarily blinded by the glare of a signal, the Closer a flare is to the objective the greater will be the illumination.

A flare above and behind the obsever will illuminate nearby objects only and will be use-less for long-range observation. A flare midway between the observer and the objective will lose effectiveness because of the distance the light must travel from ot to the ob-jective and back to the observer. A flare placed behind the objective and almost in the line of vision will be useful in silhouetting the objective, especially under conditions of slight haze. Backgrounds which offer contrast in color or brightness increase visibility, while non-contrasting backgrounds reduce it materially. The angle of observation is go-verned by the same principle as that which governs the use of mirrors; i.e. altough light is diffused equally in all directions from an unploished surface, the angle at which it lea-ves a polished surface equals the angle at which it stirkes. The following table will serve to show relative visibility and may be used as a guide.

CANDLEPOWER OF LIGHT NECESSARY FOR VISIBILITY AT 5,000 YARDS

RED

YELLOW

WHITE

GREEN

Night, clear

1.0

2.0

2.5

2.8

Night, light rain

1.2

2.1

3.0

3.2

Night, overcast and haze

3.2

4.1

3.1

5.9

Night, heavy rain

8.9

33.5

132.0

33.5

Night, light snow

222.0

835.0

1,556.0

567.0

Day, overcast and haze

2,000.0

2,111.0

3,222.0

4,000.0

Day, clear

4,778.0

7,556.0

11,110.0

10,000.0

The above table is based on a fixed distance; any variations due to distance may be cal-culated by using the inverse square formula above.

Effect of Atmospheric Conditions on Visibilty

5. Dust, humidity, moisture, or smoke will affect pyrotechnic visibility. The reds and yel-lows will be affected to a lesser degree than the greens and blues. Heavy fog, snow, or rain may totally obscure pyrotechnic lights, even at short range; and sky background may materially alter both color and ditinctness. For example, when a signal is placed bet-ween the observer and the sun, a different effect will be obtained than when the obser-ver is between the sun and the signal. Greater reflection is also apparent when low-han-ging clouds prevail.

Ammunition

6. Pyrotechnic ammunition includes flares, markers, identification signals, and illuminating or smoke-producing grenades. Colored smoke signals will also be included in this pamphlet as pyrotechnic ammunition. These items are mixtures of chemicals in powdered or solid form, packed in suitable cartridges or containers, and designed to produce certain visual effects in day or night operations. Standard ammunition contains one or more of the fol-lowing ingredients:

(a) A fuel, or burning agent, usually one of the compounds of aluminum or magnesium

(b) An oxygen supplier, one or more of the chlorates, nitratesm etc.

(c) Coloring agents, such as the salts of barium, copper, or strontium

(d) A binding agent, such as asphalt, paraffin, or other compound

In some instances barium chlorate may acts as both a coloring agent and an oxygen supplier. When using any item of ammunition, the proper firing mechanism or method of launching must be employed.

Firing Devices

7. Pyrotechnics firing devices are of three types: projectors, ejectors, and pistols. Pro-jectors are usually of the mortar type, muzzle-loaded and set off by contacting a firing pin with the primer on the propelling charge in the ammunition. Ejectors, used in subma-rines, are operated by compressed air in a manner similar to the operation of torpedo tu-bes. Several types of pistols are used in pyrotechnics. Some ammunition is self-igniting and needs no firing mechanism other than a lanyrad or trip wire to release a self-contai-ned firing pin against the primer. Grenades and hand-launched flares are ignited by relea-sing the safety lever when throwing or casting overboard.

Care of Firing Devices

8. The general rules of ordnance maintenance apply to pyrotechnic firing devices. Clima-tic conditions may affect them, however, and in arctic zones it is recommended that very little lubrication be used, as the oil may thicken and cause sluggish action. All firing devices must be cleaned after each use, and must be kept in serviceable condition at all times.