[Transcriber's Note: Bold text is surrounded by =equal signs= and
italic text is surrounded by _underscores_.]
WAR DEPARTMENT
OFFICE OF THE CHIEF SIGNAL OFFICER
MANUAL No. 6
VISUAL SIGNALING
SIGNAL CORPS UNITED STATES ARMY
1910
[Illustration]
WASHINGTON
GOVERNMENT PRINTING OFFICE
1910
WAR DEPARTMENT,
Document No. 366.
OFFICE OF THE CHIEF SIGNAL OFFICER.
WAR DEPARTMENT,
OFFICE OF THE CHIEF OF STAFF,
_Washington, April 20, 1910_.
The following Manual of Visual Signaling, prepared in the Office of
the Chief Signal Officer, is approved and herewith published for the
information and guidance of the Regular Army and the Organized Militia
of the United States, and supersedes all other pamphlets or similar
instructions heretofore issued upon the subject. Officers and men
of the Signal Corps will thoroughly familiarize themselves with the
instructions and suggestions contained herein.
By order of the Secretary of War.
TASKER H. BLISS,
_Brig. General, General Staff,
Acting Chief of Staff_.
TABLE OF CONTENTS.
Page.
CHAPTER I.--INTRODUCTION 9
CHAPTER II.--_Visual signaling equipment._
The wand 11
The flag kit:
The 2-foot flag kit 12
The 4-foot flag kit 12
Care of flag material 13
Powers and limitations of flag signaling 13
The heliograph:
Historical 14
Description 14
Assembling 17
Adjustment 20
Operation 21
Care of apparatus 22
Powers and limitations of the heliograph 22
The signal lantern:
Acetylene 23
Calcium carbide 23
Method of gas generation 24
Description 25
Operation and care 30
Powers and limitations of the signal lantern 35
Rockets and shells:
Description 35
Operation 38
Employment 40
The semaphore: Description 40
The searchlight: Methods of employment 41
The Coston signals 41
Very's night signals 42
The Ardois system of signaling 42
Sound signals 44
Improvised signal methods 44
CHAPTER III.--_Alphabets or systems of signals._
Signal alphabets:
American Morse 45
Continental Morse 45
Army and navy 45
Abbreviations 46
Code calls 47
Execution of signal alphabets 47
The army and navy alphabet 47
The Morse alphabets 49
International code of signals:
Description 51
Two-arm semaphore 51
The Ardois system 52
Coston signals 54
Very's night signals 54
Rocket signaling 55
Two-arm semaphore alphabet, U. S. Navy 57
Summary of signals, army and navy alphabet 60
CHAPTER IV.--_The field message._
Definition 64
The blank form 64
Writing the message 66
Instructions to operators:
Use of message blank 66
Duties of sending operators 66
Order of transmission 66
Duties of receiving operators 67
Communications confidential 67
Checking the message 67
CHAPTER V.--_The signal station._
Location of stations:
General considerations 68
Backgrounds 70
Azimuth of stations 71
Altitude 71
Determination of background color 72
Choice of apparatus 73
Miscellaneous considerations 73
Intervisibility table 74
Finding a station 75
Operation of stations:
Personnel 76
Calls and personal signals 78
Opening communication 79
Commencing the message 80
Sending and receiving 80
Breaking 80
Discontinuance of transmission 81
Acknowledgment of receipt 81
Station records 81
Formation of signals 82
Repeating the message 83
Signal practice 83
CHAPTER VI.--_Codes and ciphers._
Codes in use 84
Employment of codes 84
Cipher code 85
The War Department Code 86
Cipher code in field work 87
Field ciphers:
Description and use 87
Forms of field cipher 88
Inversions 88
Concealment of terminations 88
Cipher apparatus: The cipher disk 89
The mathematical cipher 93
The route cipher 94
Cipher detection: Employment of cipher disk 96
CHAPTER VII.--_Field glasses and telescopes._
Reflection 98
Refraction 98
Lenses 98
Focus 99
Optical center 99
Image 99
Conjugate foci 99
Law of foci 100
Formation of image 101
Spherical aberration 102
Chromatic aberration 102
Telescopes 104
Galilean field glasses and telescopes 106
Porro prism field glasses and telescopes 106
Field glasses 108
Properties of telescopes and field glasses 109
Power 109
Light 111
Field 114
Definition 115
Field glasses and telescopes issued by the Signal Corps 119
Type A 121
Type B 124
Type C 125
Type D 125
Field-glass specifications 126
CHAPTER I.
INTRODUCTION.
While, in consequence of the development of electrical invention and
improvement, visual signaling will be less frequently resorted to in
future than heretofore in the service of field lines of information,
it should be appreciated that the necessity for an adequate supply
of apparatus of this kind, and the need for skilled manipulators to
operate it, has in no wise diminished. The great celerity with which
electric signals can be exchanged and their usual entire independence
of local conditions has placed systems of this class foremost among
the signaling methods of the world. There is scarcely any commercial
industry whose successful existence does not vitally depend upon some
one, perhaps several systems of signaling, and improvements of old and
inventions of new signal devices are continually necessary to meet the
requisite needs demanded by the progress of art and science. Railways
are probably the greatest of all commercial users of signals. With them
the great mass of intelligence is transmitted by the electric telegraph
and telephone, but the flag, the semaphore, the signal light, and
many other contrivances furnish indispensable visual adjuncts. Visual
signaling is and always will be a most valuable means of transmitting
information in peace and war, and it is not to be imagined that it
will ever be supplanted in its particular function by the introduction
of other methods. Occasions will frequently occur in the field when
no other means will be practicable, and then, if not before, will the
value of the system be fully emphasized.
Strictly speaking, a visual signal is any visible sign by which
intelligence is communicated, but in a military sense the term
visual signaling has a broader meaning and includes other methods of
transmitting information than those which appeal to the sense of sight.
In most systems of signals suitable for military use, each signal is
composed of one or more separate units, known as elements. Having
prescribed a certain number of elements, the various signals are
formed by having these elements appear singly or together in different
arrangements or combinations. The continental system is one of two
elements, namely the dot and the dash, while the Morse system employs
three elements, the dot, the dash, and the space. Having agreed upon
a certain number of combinations of elements, a system of signals is
formed by giving a meaning to each combination. These meanings usually
include the letters of the alphabet and numerals, combinations of which
being used to formulate necessary information. Combinations of elements
of any system can also, however, be used to indicate any desired
meaning.
With reference to period of visibility, signals are of two kinds,
transient and permanent. A transient signal is one which disappears as
soon as completed; a permanent signal is one that remains in view for
some time. Heliograph signals are transient signals, while signals made
by code flags are permanent signals. Signals are divided into classes
in accordance with the number of elements employed in their formation.
Thus, signals using two elements are signals of the second class,
signals using three elements signals of the third class, etc.
The standard apparatus used in visual signaling is fully described in
a succeeding chapter. Some of the instruments employed are used wholly
for day, and some wholly for night, signaling. Some devices, either
with or without slight variations, are equally well adapted to day or
night work. Visual signaling presents a great field for ingenious and
resourceful work, and emergency will often demand the advantageous
employment of other methods than those described herein.