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Ship Camouflage
Instructions
United States Navy
Ships - 2
Revision 1
Bureau of Ships
September 1941
Discussion of Ship
Camouflage
References.
Reference 1:
Bureau of Construction and Repair Confidential
Publication - "Handbook on Ship Camouflage" (Short Title - C and
R. 4) 1937.
Reference 2:
Naval Research Laboratory Report H-1585, January
12, 1940, "Naval Camouflage, Tests at Sea, June to September,
1939," and references therein.
Reference 3:
Comdesbatfor Conf. Ltr. to Buships, 25 October
1940, S19 - Ser. 4888, "Camouflage of Destroyers - Low Visibility
Paint."
Reference 4:
Comdesdiv. 17 Conf. Ltr. S19/FB17, 7 March 1941;
FB17/S19/A16-3, 13 may 1941.
Reference 5:
Comdr. Lexington Air Group Conf. Ltr. CLAG/S19/(ts)
(231) 6 June 1941.
Reference 6:
CinClant Ltr. S19/0581, 26 June 1941; 4Cl-41, 19
July 1941.
Reference 7:
CinCpac Ltr. S19/(50) Serial 01445, 13 September
1941.
Reference 8:
Naval Research Laboratory Report H-1598, March 14,
1940, "tests at Sea of February, 1940, in the Key West Area of the
Visibility of Submarines and Transparency Measurements of Navigable
Waters." Comsubfor. Ltr. to Buships, FF4/A4-3/S19, 3 September
1940.
Results
of Surface Ship Camouflage Experiments.
The results from earlier investigations of many
aspects of surface ship camouflage by the Bureau of Construction and Repair
were summarized in reference 1. Investigations continued since that time
are described in references 2 to 8. The tests of references 2 and 3
culminated in the preparation of the First Edition of this booklet in January
1941. Some of the more important facts on which the measures of the
First Edition were used are:
- That
a darker color is of low visibility to aerial observers in all type of
weather because of sea background, but is relatively visible to surface
observers because of sky background, and yields some course
deception to surface observers because shadows are not prominent.
- That a light color is of low visibility to surface observers in hazy and foggy weather.
- That a graded system produces some range
deception.
- That bold dazzle camouflage was undesirable
because of enhanced visibility.
- That unobtrusive dazzle camouflage yielded some
deception without too great enhancement of visibility, but was limited in
its application.
- That all camouflage is ineffective against the sun
or other concentrated source of illumination.
- That camouflage for low visibility is more
successful on small ships than on large ships.
- That wakes and smoke may neutralize any advantage
gained by paint.
The measures of the First Edition employed three
shades of gray, a Dark Gray, a Medium Gray, and a Light Gray (Standard Navy
Gray of 1928 - 1940). Subsequent experiments, references 4, 5, 6 and 7
led to the conclusion that the Dark Gray was too dark and the Light Gray too
light., and that Blue Gray colors would be better than pure Gray colors.
The Blue Gray colors were selected, those of Plate
12, and Measures 11 to 14
are based on them. Another change was made based upon reference 6.
In the First Edition, Measure 2 was a graded system in which the hull of the
ship was painted with three stripes, of Dark Gray at the waterline, Ocean Gray
next above, and Light Gray above that. This measure has been replaced by
Measure 12 in which the dark color Sea Blue is carried from the waterline to
the main deck, with Ocean Gray above this on the Superstructure masses and
haze Gray on pole masts and small projections. Measure 12 departed
considerably from the original conception of a "graded" system, in
which grading was carried out entirely on the hull.
Experiment showed, references 5, 6 and 7, that
certain measures of the First Edition were ineffective,
namely, Measure 5,
painted bow waves for speed deception, and Measures 6, 7 and 8, artifices of
painting a ship to look like another ship of another class or type.
Accordingly, these measures have been omitted in the present revision.
Discussion
of Measures 11, 12, 13 and 14.
Based on the preceding section the following remarks
may be made concerning Measures 11, 12, 13 and 14.
Measure 11, Sea Blue, has not been tested.
However, its effectiveness may be said to be known approximately, and to be
about the same as, or perhaps better than, the darker pure gray system which
has been tested.
Measure 12, graded, has not been tested.
However, its effectiveness may be said to be known approximately and to be
about the same as, or perhaps better than, a system not greatly different
which has been tested by the Commander-in-Chief, Atlantic Fleet. The
system consisted of Sea Blue to the sheer line, Ocean Gray to the top of the
high turrets including stacks and Haze Gray above, (reference
6).
Measure 13, Haze Gray, has not been tested, but
inasmuch as it is intermediate in brightness between Ocean Gray and Standard
Navy Gray of 1928 - 1940, its effectiveness may be said to be known
approximately.
Measure 14, Ocean Gray, has been tested and its
effectiveness is known.
Table 1 gives the approximate effectiveness of the
various systems. In fact, Table 1
gives about the only clear-cut
conclusions which can be drawn in the light of present knowledge.
Table
1 - Approximate Effectiveness of Camouflage Measures.
| Measure |
Least Visible |
Most Visible |
Deception |
Measure 11
Sea Blue |
Day: |
Aerial Observer |
Day: |
Surface Observer in
Clear of Hazy Weather |
Course Deception |
| |
Day: |
Against Dark
Cloud Bank |
|
| Day: |
Dark Smoke Screen |
| Night: |
When in Searchlight |
| Night: |
Moon Behind Surface
Observer. |
| |
Measure 12
Graded |
|
A Compromise, Moderately
Low Visibility to Aerial and Surface Observers. |
|
Course and Range Deception and Ship
Identification. |
| |
Measure 13
Haze Gray |
Day: |
Surface Observer in Hazy, Foggy Weather. |
Day: |
Aerial Observer |
|
| |
Night: |
No Moon. |
Night: |
When in Searchlight. |
| |
Measure 14
Ocean Gray |
Day: |
Surface Observer in Bright Sunny Weather. |
|
| |
Night: |
Moonlight |
Discussion
of Splotch Patterns.
A pattern of splotches for disturbing course
estimation is completely ineffective in shadow. Its effectiveness, if
any, depends on the illumination and condition of observation. These
factors are so variable that no particular pattern can claim an advantage over
any other pattern. This is the reason that the directions in Chapter 3
for painting the spots are indefinite. In general it is better to paint
the lighter colors on areas which are usually in a shadow and the darker
splotches on areas usually in the light. The splotch patterns of Plate 19 have not been tested. Finally, it is true that although
patterns of spots have been painted frequently on ships, there is no first
hand information concerning their effectiveness.
Discussion
of Measure 9 for Submarines.
Experiments off Key West, in the Canal Zone, and in
Hawaiian waters with submerged submarines observed from the air, reference
8,
showed in general that a dark color was the color of lowest visibility,
and in particular that a dark blue was slightly less visible than black.
The experiments were not sufficiently extensive to decide whether the slight
difference was of essential importance. It turned out that the earlier
formulations of the dark blue paint, called "Pearl Harbor Blue",
deteriorated and turned milky in a few weeks, whereas the black paint remained
serviceable for several months. Therefore, black paint is specified in
Measure 9. Improved formulas of Blue are being tested extensively in the
fleet at present. A special kind of colloidal painting for the purpose
of reducing the visibility of the vertical surfaces (conning tower) of a
submarine on the surface is being investigated by Comsublant and the
Commandant First Naval District.
Discussion
of Visibility of a Surface Ship at Sea.
The infinite variety of background against which
ships are seen as a result of varying light and cloud effects will always make
camouflage a controversial subject until a means is found to color a ship at
will. All that can be expected is the color which is effective most
often against the observer whom it is most important to evade. It is of
interest to discuss a few well known general facts about the visibility of a
ship at sea; a complete discussion of all cases would be tedious. The
visibility of a ship at sea depends on its contrast with the background, and
this in turn depends on its contrast with the background, and this in turn
depends on a number of factors, the more important of which are the color
of the ship and the background, the distance from the observer, the
height of the observer above sea level and on the amount and character of the
illumination.
Some of factors are illustrated in Plates 20 to 25,
which give the appearance of a ship at various ranges to an observer at
various altitudes above sea level. Plates 20 to 24 are drawn to scale,
and if looked at from a distance of about 30 feet are true to size.
As shown in Plate 20, to an observer not more than
about 20 feet above sea level as on a submarine, practically the entire ship
appears against the sky for all ranges above a few miles. Hence for low
visibility the ship should in general be a light color; a dark colored ship
will be most visible but may give course deception because of the
indistinctness of shadows.
Plates 20, 21 and 22 for altitudes of the observer of
20, 60 and 180 feet, respectively, illustrate the case of the observer on a
surface ship and show that the ship appears against either a background of sea
and sky, or of sky alone. In this case a ship painted with some type of
graded system may occasionally be less visible than a ship painted a solid
color. In addition a graded system may confuse the position of the
waterline relative to the horizon and may yield range deception.
Plates 23 and 24 for altitudes of 1000 and 5000 feet,
respectively, illustrate the case of the observer in the air. he views
the ship against the sea at all ranges. Since the sea is fairly dark,
except toward the sun and in the rare condition of mirror calm, the ship
should be painted a dark color for the lowest visibility.
The effect of the relative bearing of the sun on the
visibility of a light color ship and a dark color ship is illustrated in Plate
25. The observer is at the center of the circle, and the altitude of the
sun is taken to be between 20 degrees and 40 degrees. The ships are
assumed to be always broadside to the observer; this is a simple case.
The outside circle of ships appears against the horizon sky and hence refers
to an observer near sea level. The inside circle of ships appears
against the water and hence refers to an observer in the air. Toward,
the sun both the light ship and dark ship are always darker than the
background. whether the background is sky or water.
In the case of the sky background the dark ship is
too dark at all bearings from the sun. Opposite the sun the light
color ship may be too light, and if so, there is an intermediate sector in
which the light ship may approximate the sky background in brightness and be
of low visibility. The width and position of this sector depends on the
reflectivity (brightness) of the paint of the light color ship.
In the case of the sea background, in the sector away
from the sun the dark ship may approximate the background brightness and be
less visible than the light color ship. There is another smaller sector,
however, more or less toward the sun in which the dark ship is too dark and
the light ship is the least visible.
More complex cases arise if the ship is not broadside
to the observer. Such cases being perfectly obvious would be tiresome to
consider in detail, and similarly for cases of a partly cloudy sky.
Camouflage
Paint.
All camouflage paint
must be mat or dull, not glossy, and specification must be made of the maximum
allowable amount of gloss. Other optical qualities of the paint which
require specification are its color and reflectivity.
Color.
A practical method of recording the color is
by means of the Munsell Book of Color.* The specification that a
certain is "Munsell PB 5/2" means that under daylight illumination
the paint matches color and brightness the colored rectangle in the Munsell
Book of Color on page "Purple Blue", row 5, column 2. The
spectrophotometric curves of all the color samples of the Munsell Book have
been determined by the United States National Bureau of Standards, and the
colors are therefore reproducible at any future time. The Munsell
notations of the camouflage colors are given in Table
2.
*Abridged Edition, 1929, Munsell Color
Company, Inc., Baltimore, Maryland. The Munsell color charts provide the
best working standard available at present.
Table
2. Data of Camouflage Colors
| Name |
Formula |
Munsell |
Reflectivity |
Gloss |
| Deck Blue |
20-B |
PB 3/4 |
7 Percent |
14 |
| Sea Blue |
5-S |
PB 4/4 |
11 Percent |
17.5 |
| Ocean Gray |
5-O |
PB 5/2 |
17 Percent |
12 |
| Haze Gray |
5-H |
PB 6/2 |
28 Percent |
12 |
Reflectivty.
The diffuse reflectivity of a painted surface for
white light is a convenient and often used method of describing the lightness or
darkness of the surface. The reflectivity is the ratio of the total
amount of white light diffusely reflected by the surface to the amount falling
on the surface. The reflectivity of a black surface is zero and of a
white surface is 100 percent. Magnesium carbonate has a reflectivity of
about 98 percent and and is a practical standard of a non-glossy white.
The reflectivities of all the Munsell colors are tabulated on the
unabridged edition and therefore if a color is specified on the Munsell
system its reflectivity is known automatically. But in order to avoid
looking up the Munsell table it is often desirable to give the reflectivities
in addition to the Munsell notation. The reflectivities of Deck Blue,
Sea Blue, Ocean Gray and Haze Gray are listed in Table
2. The
reflectivity of a surface does not of course specify its color; for example on
may have a red surface and a blue surface of the same reflectivity.
However, in dealing with a series of different shades of approximately the
same color, as in the case of the camouflage colors, the reflectivity gives a
fairly satisfactory numerical description of their lightness or
darkness. It is of interest to recall that Navy Standard Light Gray
paint of the years 1928 - 1940 had a reflectivity of about 40 percent, and
this was considerably lighter than the present Haze Gray.
Gloss.
A low gloss is desirable in camouflage paints to
avoid highlights or bright reflections from the surfaces in sunlight or the
beam of a searchlight. Gloss is the property of a surface to reflect
light SPECULARLY, which means like a mirror. A surface which is not
glossy is said to be MAT. There is no accepted definition or scale of
gloss; several arbitrary scales are available which depend upon the particular
instrument selected to measure the gloss. A convenient scale is based on
the ratio of the amount of light reflected at an angle of 45 degrees from the
surface in question to the amount reflected at the same angle from a surface
of polished black glass. On this scale the gloss values of the
camouflage paints, freshly painted, are entered in Table
2. The gloss
value of a camouflage paint should be below about 20 percent to avoid
undesirable bright reflections or "Highlight". The Navy
Standard Light Gray paint of 1928 - 1940 had a gloss of about 44 percent which
weathered to about 28 after thirty days exposure.
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