of aircraft at night. The apparatus for this aerial sound-ranging
consists of large sound-gathering instruments which are used to
direct search-lights in the location of approaching airplanes. When a
bombing-plane approaches at night the hum of the motor can be heard at a
distance of from one to three miles or more, depending upon the direction
of the sound and the atmospheric conditions. The direction of sound,
however, particularly when it originates in the sky, is illusive to the
naked ear and search-lights were obliged to sweep the heavens in the
general direction from which the airplane was believed to be approaching,
in an endeavor to locate it. By the use of these detectors, however, the
sound of an airplane can be detected at a considerably greater distance
than by the naked ear, and, what is even more important, its direction
can be determined within a very small angle—less than five degrees. In
this way the area over which the search-light has to sweep is greatly
reduced, and the chances of locating the aerial marauder are enormously
increased.
Extensive experiments have been conducted in this country by the Engineer
Corps in the development of these aerial sound-detectors. One form
consists of four horns, two in a vertical and two in a horizontal plant,
with listening-tubes leading from the small ends to the receivers of the
observer’s head-set. These horns are mounted so as to permit rotation
on a horizontal shaft and turning on a plane-table, the whole being
supported on a sort of steel tower which, owing to its height and the
fact that it cannot easily be moved, affords a rather conspicuous target
for the enemy. The obvious disadvantage of this type is recompensed in
a measure, however, by its accuracy and by the fact that it will so
magnify a sound that the operators can hear the tick of a watch a hundred
and fifty yards away. This apparatus is, however, large and cumbersome,
and though excellent for seacoast and fortress defense, is not adapted
for use in the field, where extreme mobility is required. For this
latter purpose paraboloid sound-reflectors have been developed. These
paraboloids are about nine feet in diameter, made in sectors of material
similar to beaver board, and look like enormous editions of kettles used
for boiling soap. They can be taken down and packed into small space for
transportation, and are easily set up; being mounted on Ford chassis,
they can go anywhere that a “flivver” can go. The paraboloids, like the
horns, are directed by balancing the sound so that it is equally audible
in both ears. These instruments have a sensitiveness double that of the
unaided ear and by means of them a sound can be located to within three
degrees.
When the officer in charge of one of these sound-detectors hears
through the receivers of his head-set the rhythmic hum which denotes
an approaching airplane—and I might mention, parenthetically, that
experienced observers can tell with almost absolute certainty not only
the nationality of the approaching machine but even the type and power
of its engines—he orders several sound-readings to be taken at definite
intervals of time. With these readings as a basis for the calculation,
the probable location of the airplane at the end of the next time
interval is plotted and the search-light is flashed in that direction
just long enough to locate the machine. Quick work is required, however,
for the airplane often travels at a hundred miles or more an hour and may
abruptly change its course at any moment. Then, the plane once spotted,
the beam of the search-light never leaves it, and the waiting crews of
the antiaircraft guns get to work. Experiments are now being conducted
to enable these listening devices to be used in synchronization with
search-lights, so that, when the light is flashed, the airplane will be
within the beam and no indication of the presence of the search-light
will be given the aviator until he finds himself illuminated as a
spot-light follows the movements of a dancer on a darkened stage.
In the autumn of 1917 the National Research Council, at the request of
the Chief of Engineers, inaugurated an extensive series of search-light
investigations, which, thanks to the enthusiastic co-operation of
scientists, manufacturers, and certain government bureaus, resulted
in a number of remarkable developments. Eighteen different kinds of
search-lights were developed during these experiments, the first being
placed in operation in France in October, 1918. This represented an
entirely new form of light, more powerful than any heretofore produced
by any nation. It weighs about one-eighth as much as the most powerful
search-light theretofore produced, costs only about one-third as much,
and has about one-quarter the cubage. Other improvements now in progress
give assurance that its range will be doubled, its cost still further
reduced, and its mobility greatly increased. And, what is of almost equal
importance, the designs are now becoming so simplified that production
need no longer be confined to highly specialized shops, but may be
distributed over the country to all classes of machine manufacturers,
thus making it possible to produce a large quantity in a relatively
short time. With this new equipment the United States will possess a
search-light having an effective range approximately twice that of the
best search-light produced before the war, with four times as great a
field. Two features of the latest types of lamps are particularly worthy
of notice. These are, first, the “dish-pan” type of light, the chief
characteristic of which is that it has no lens; and, second, the metal
mirror, which is much more easily manufactured, is far less fragile,
costs only a third as much, and possesses almost as great reflecting
qualities as the glass ones.
The search-light used by the American forces for antiaircraft work is
the heavy 60-inch seacoast type—the largest light known—lightened and
modified for use in the field, with a range of practically 30,000 feet.
As the result of recent experiments it has been found that the visibility
at 12,000 feet was 85 per cent, while at 15,000 feet, or nearly 3 miles,
it was 43 per cent. In order to obtain these standards of comparison for
visibility for search-lights, an aviator was directed to fly back and
forth through the beam a certain number of times. If the observers on the
ground recorded the full number of passages across the beam, 100 per cent
was registered, this occurring regularly at 5,000 feet, and in most cases
during tests at 8,000 feet. The percentage of visibility was, in other
words, the number of times the airplane was seen to the number of times
it crossed the beam.
* * * * *
When warfare of movement becomes stabilized into position or trench
warfare, it is almost certain that, sooner or later, one side or the
other will resort to some form of underground attack. To permit of this
subterranean warfare, certain conditions are requisite: the lines must be
fairly close together, the level of the ground-water must be deep, and
the ground itself must not be too hard. These obstacles to successful
mining are not insuperable, however, for, preparatory to their assault on
Messines Ridge, the British drove a tunnel which was a mile in length,
and on the Carso I saw Italian engineers driving their galleries through
solid rock. France and England early recognized the importance of this
form of warfare and organized their miners accordingly, and, upon our
entrance into the war, we too organized and sent to France a mining
regiment—the 27th Engineers. It is estimated that by the summer of 1918
there were upward of 40,000 skilled miners on the Western Front, these
soldiers of the pick and drill having been brought from the remotest
corners of the earth—from the Yukon, the Rand, and the Congo, from
Mexico, Australia, and California. In my “Vive la France!” I told, if I
remember rightly, of the Cornish miners, known as “kickers,” who lay on
their backs, as they do in the tin mines in Cornwall, where the galleries
are so low that there is no room to swing a pick, and kicked away the
earth by means of a sort of spur attached to their heels.
The officers of the American mining regiment were engineers who had
had practical experience in all those far-off regions where men seek
their fortunes in the earth. One of them, a young lieutenant, was
diamond-mining in the Katanga district of the Congo when word reached him
by native runner that the United States had decided to take a hand in
the Great War. It took him four months of uninterrupted travel by horse,
wagon, rail, and boat to reach the United States and offer his services
to the Chief of Engineers. Another of our mining officers was a prisoner
of the revolutionists in Mexico when the rumor penetrated to his prison
cell that the United States had gone to war. That night he overpowered
his guards, scaled the prison wall, made his way on foot across northern
Mexico, the journey being relieved from monotony by several hairbreadth
escapes from bandit bands, and reached the border in time to join the
Engineers and go to France with one of the first contingents.
In former wars military mining was almost wholly confined to siege
operations; that is, driving galleries under fortified positions and
blowing them up. But the Great War developed an entirely new system
of mining tactics, which included frontal and flank attacks, raids,
enveloping movements, and other phases of war as fought on the surface
of the earth. “Unlike the soldier who fights above ground,” explained
a mining officer, “the miner has to be prepared for attacks not only
against his front and flanks, but for assaults which may come from
overhead or from underneath. In other words, he has four flanks to defend
instead of two.”
A typical mining position, such as would be prepared on an active sector
of the front, would consist of an upper level having a series of forked
galleries, known as “feelers,” with geophone listening-posts at their
extremities, and a deeper level, with numerous “fighting branches”
projecting from it, to protect the lower flank. Just as the sentries
in the trenches strained their eyes to detect any ominous figures in
the darkness of No Man’s Land, so the mining sentinels, crouching over
their geophones in the headings of dim-lit galleries, strained their
ears to catch the faint sounds which gave warning that the enemy was
approaching underground. The geophone, which has proved of incalculable
value in mining warfare, is an instrument for augmenting small sounds
coming through the ground. The American geophone, which is a highly
sensitive, extremely simple, and easily portable instrument, is in no
sense an electrical device, resembling, rather, the stethoscope used by
physicians for testing the lungs. In mining operations two geophones
are used, one for each ear, the instruments being so sensitive that the
sounds caused by a fly walking on the wooden support of the geophone
appear as loud as the tramp of a horse on the floor of a stable. If a
sentinel on duty in an underground listening-post caught through his
geophone a sound which was more distinct in, say, his right ear than
in his left, he gently shifted one of the instruments, inch by inch,
until the sound was the same in both ears. Then, by means of a compass,
he took the magnetic bearing of a line perpendicular to that passing
through the two geophones, which would give the direction from which the
sound came. Meanwhile sentries in the other listening-posts were doing
the same thing, so that, by the co-ordination of their reports and by
triangulation, the enemy’s gallery could be located within a few yards.
If the mining officer was convinced that the enemy was driving a gallery
for the purpose of putting a mine under his position, two courses of
action would be open to him. He could remain on the defensive and check
the enemy’s advance by the use of “camouflets,” this being the name
applied to explosive charges which expend their force laterally, thus
destroying the enemy’s gallery without causing a crater; or he could
resort to strategy and engage the enemy’s attention at one point by
exploding camouflets or by working noisily, and under cover of this
diversion drive a fighting gallery toward his flank elsewhere. If,
instead of being content to remain on the defensive, the officer in
charge of mining operations decided to assume the offensive, he would
engage the enemy’s attention at one point, either by exploding camouflets
or by working noisily, and at the same time drive a fighting gallery
toward his adversary’s flank. In this latter case the most profound
silence had, of course, to be enforced in the fighting branch if the
enemy’s geophones were not to give warning of its approach. No talking
was permitted, the men wore felt-soled shoes and worked with trowels
instead of picks, and the earth was carried out in cars with rubber
tires. So silently were the operations in the fighting branches conducted
that they would frequently break into the enemy galleries without the
slightest warning, whereupon would ensue a struggle fought scores of
feet beneath the surface of the earth, by combatants armed with picks,
pistols, bombs, and knives, and illuminated only by flickering miners’
lamps—a battle so weird and strange in its character and setting that it
seemed like the creation of a motion-picture writer’s brain.
One of the essentials for the success of a mining operation is the
concealment of the spoil—_i. e._, the excavated earth—which, if piled
in a heap at the entrance to the workings, would almost certainly
be photographed by aerial observers, thus informing the enemy, as
unmistakably as though it were announced on a placard, that a mining
gallery was being driven. The French, in order to hide the spoil from
their mining operations, conceived the ingenious plan of digging a
shallow trench, usually only a few inches deep, and lining it with black
paper, so that when photographed from an airplane it produced the effect
of the black shadow cast by a trench of customary depth. They would then
distribute the spoil from their subterranean galleries along the sides
of this false trench, so that it appeared in the photograph to have been
thrown up from it.
* * * * *
Dugouts have become such a commonplace in the past four years that
few, save the miners themselves, gave much thought to or had more than
the haziest ideas of the time, skill, and labor required in their
construction. Take yourself, for example. You have read about dugouts
and seen pictures of dugouts and have probably had relatives or friends
living in dugouts. How long, then, think you, would it take a force
of skilled miners to complete a front-line dugout large enough to
accommodate a half-platoon? (For your information I might explain that
such a dugout is 35 feet long, 9 feet wide, and 6 feet high, with 17
feet of overhead cover.) Using all the men that could be employed, and
working from nightfall until dawn, it would require at least three months
to complete such a dugout. If in the rear area, where the men could be
worked continuously in shifts, it could be completed in about thirty days.
[Illustration: NEW TYPE OF SEARCH-LIGHT USED IN THE AMERICAN ARMY.
The steel tower is collapsible and light and, being mounted on a
motor-truck, is extremely mobile.]
[Illustration: CAMOUFLAGING A DIVISIONAL HEADQUARTERS IN THE TOUL SECTOR.
Constructing the screen.
The screen as it appeared upon completion.]
A recent and little-advertised development of trench warfare was the
introduction of “mobile charges.” These consisted of packages of high
explosive in ten, twenty, or thirty pound sizes, which were used by
assaulting troops for destroying dugouts, much as depth bombs were used
by the navy to destroy submarines. With the increasing use of mobile
charges it became necessary to design dugouts which would be proof
against them. In this work, which was carried on by the Mining School,
extensive use was made of dogs, experiments having shown that explosions
which will rupture the lung-tissues of a dog will similarly affect those
of a human being. Thanks to the knowledge thus obtained at the cost of
canine lives, a type of dugout construction was perfected which afforded
the occupants comparative immunity from mobile charges and hand-grenades.
An ingenious receptacle for this latter form of enemy visiting-card was
the “bomb-pit,” which was a sort of small cistern, built at the foot
of the dugout stairs, into which a hand-grenade would fall and explode
harmlessly.
Though it has no direct relation to the work of the American Mining
School, I might mention, as an illustration of the part played by miners
in the great conflict, that when the British in 1917 blew off the entire
top of Messines Ridge prior to their assault on that position, 19 mines,
containing a total of 950,000 pounds of ammonal—equivalent to 1,580,000
pounds of dynamite—were exploded simultaneously. A single one of these
mines contained 95,000 pounds of ammonal and made a crater 186 feet wide
and 125 feet deep.
* * * * *
Though few activities of the Engineers were more important than the work
of the Camouflage Section, and though certainly none was more picturesque
or interesting, it is with some diffidence that I introduce the subject,
for I am perfectly aware that American readers have been, to make use of
a British colloquialism, “jolly well fed-up” on everything pertaining to
camouflage. The point is, however, that they have been largely “fed-up”
on misinformation. They have read hundreds of magazine articles and
newspaper stories about fake trees and papier-maché horses and the like,
but of the real work of the Camouflage Corps—which, as an American
general remarked, was “as practical as machine-guns and as necessary
as ammunition”—they have heretofore been permitted, for quite obvious
reasons, to know next to nothing. Certain camouflage operations on the
American Front were of such vital importance to the success of our armies
that, far from acquainting the public with them, they were veiled in the
profoundest mystery.
Military camouflage is a development of the Great War and has, therefore,
no history and little literature. It differs from the purely scientific
work of engineering, which has few variants and in which nearly all
problems can be worked out by formula, in that it has countless variants
of light, color, and position, and each problem of concealment is an
individual one. Upon the entry of the United States into the war, much
study was devoted to French and British camouflage methods, both in the
factory and in the field. The British, it was found, did nothing without
the most careful scientific investigation, which included aerophotography
of all materials, while the more careless and temperamental French relied
rather on their innate artistic sense of form and color. By combining the
best features of both systems and strongly tincturing them with American
energy, ingenuity, and manufacturing methods, our Camouflage Service
soon came to be recognized as the best equipped and most efficient in
the Allied Armies. At Dijon, in the Department of the Haute-Marne, we
established a huge plant, known as the Central Camouflage Factory, where
a hundred soldiers and some nine hundred Frenchwomen were employed in the
production of materials, while at the Army Camouflage School of Fort St.
Menge, near Langres, practical instruction was given in the use of these
materials in the field.
When the war ended, the American Camouflage Service consisted of a
battalion of the 40th Engineers—which was on the point of being expanded
into a regiment—under the command of Lieutenant-Colonel H. S. Bennison,
with Evarts Tracy, one of the foremost architects in America, as major.
Captain Homer Saint-Gaudens, a son of the famous sculptor, was in charge
of the camouflage work of the Second Army, and Captain John Root, whose
father was architect of the Colombian Exposition, was in charge of all
camouflage work for the army artillery, he being largely responsible for
the remarkable developments in this branch of warfare. The director of
the Camouflage School at Fort St. Menge was Lieutenant Wilford S. Conrow,
the noted portrait-painter. Another officer of the battalion, Lieutenant
Harry Thrasher, a graduate of the Ecole des Beaux-Arts and a winner of
the Prix de Rome, was killed while doing camouflage work at Fismes, as
was Sergeant Everett Herter, a son of Albert Herter, the artist. Because
of the exacting nature of its requirements, the Camouflage Service
had, perhaps, a more highly educated enlisted personnel than any other
organization in the army. Among the men wearing the uniforms of privates
in the corps was the landscape-architect who laid out the grounds of
the San Diego Exposition, the stage-manager for Maude Adams, the head
property-man of the Universal Film Company, and Louis Tiffany’s chief
designer. One of the instructors at the school was a successful osteopath
who in his younger days had been a scene-painter; another was a sculptor
whose statues may be seen in many American museums and parks.
Figures are, as a rule, dry reading, but they provide the best means I
know of giving some idea of the magnitude of our camofleurs’ operations.
During the summer of 1918 the Camouflage Section used materials _per
month_ as follows:
12,000 fish-nets.
50,000 pounds of wire.
700,000 gallons of paint.
2,160,000 square yards of poultry-netting and approximately
1,000 acres of burlap.
The best and most concise rules which I have seen for the erection
of camouflage and for the enforcement of camouflage discipline are
contained in secret instructions issued in July, 1918, by the commander
of the German First Army. They read as follows:
CAMOUFLAGE
Translation of a German Document (from French IV Army Bulletin,
August 8, 1918)
1st Army
Command of the Aviation Service
Ia-Ib
ARMY HEADQUARTERS,
July 1, 1918.
I. ESSENTIAL POINTS IN THE CONSTRUCTION OF POSITIONS.
(_a_) _General._
1. Camouflage will be completed before undertaking the
work.
2. Camouflage will be sufficiently extensive in order
that all the work required may be carried out under
its protection.
3. Faulty installation will be left in place as dummy
work and be begun over again at another point with
the necessary prudence.
(_b_) _Tracks._
1. Tracks must be as few as possible and have a natural
appearance. It is best to avoid all tracks by building
the position on roads already in existence.
2. Provide fixed access for everybody. If necessary, stake
the paths out by means of wire.
3. Extend indispensable tracks beyond the position as far
as the dummy work.
4. Use furrows as paths, do not go across fields.
5. Do not dump materials in the immediate neighborhood of
the position.
(_c_) _Color of the Camouflage._
1. Harmonize the color of the camouflage with the terrain.
Green camouflage in meadows, brown in ploughed fields,
white in quarries.
2. The upper surface of the camouflage will be alternate
light and dark tones; grass, reeds, hay, or branches
fixed in iron wire, etc.
3. Renew the camouflage in proper time; the grass and
branches fade quickly and appear light and not dark
on the photographs.
4. The position must not extend partly over one field and
partly over another, as two fields are seldom of the same
color. The furrows will be reproduced in the camouflage.
5. Camouflage materials, such as the sod removed and small
trees, will be taken at a distance of at least three to
four hundred meters from the position; place a dummy work
at a sufficient distance in order that it does not reveal
the true position.
(_d_) _Forms of Camouflage._
1. Do not raise the height of the camouflage needlessly;
the higher it is the more shadow it throws. Raise it by
means of posts during the work; bring it down by day and
lay it flat if possible; cover mainly the entries and exits.
2. Do not make a heap of the earth removed but scatter it
immediately.
3. There must be no fresh cuts visible, as marked contrasts
result from it between the light and dark surfaces, the
latter appearing as deep shadows on the ground.
4. Avoid regular shapes and rectangular outlines.
5. Do not change natural shapes. Positions in fills and
embankments must not change the form of the fill or
embankment.
6. Use the roads, fills, embankments, slopes, sunken roads,
edges of woods to greater extent. Deceive the enemy by
false tracks ending in woods.
II. MAIN INSTRUCTIONS FOR COLUMNS.
(_a_) Resting columns, location, and nature of halting-places.
The most important thing is that the halting-places be
of irregular form.