INCENDIARY MATERIALS
Since it is generally known that white phosphorus, when exposed to
the air, takes fire spontaneously, it logically follows that numerous
suggestions should have been made for using this material in incendiary
devices. Practice, however, has shown that, while phosphorus is
undoubtedly of value against very easily ignitable materials, such as
hydrogen in Zeppelins, or the gasoline tanks of aeroplanes and dry
brush or grass, it is of much less value when wood and other materials
are considered. This is partly because of the low temperature of
burning, and partly because the product of combustion (phosphoric
anhydride) is really an excellent fireproofing substance. In view of
this, phosphorus was used primarily for smoke production.
A superior incendiary material is found in thermit, a mixture of
aluminum and iron oxide. When ignited, it produces an enormous amount
of heat very quickly, and the molten slag that results from the
reaction will prolong the incendiary action upon inflammable materials.
When used alone, however, it has the disadvantages that the incendiary
action is confined to a small area and that the heat energy is wasted
because of the fact that it is so rapid in its action.
For this reason it is customary to add a highly inflammable material,
which will become ignited by the thermit and will continue the
conflagration. Petroleum oils, carbon disulfide, wood distillation
products and other inflammable liquids were thoroughly tested for this
purpose. The final conclusion was reached that oil, solidified with
soap (sodium salts of the higher fatty acids) by a special method
developed by the Chemical Warfare Service, was by far the best material
to be used. In certain tests, using a combination of thermit and solid
oil, flames fifteen feet high were obtained, which would be very useful
against walls, ceilings, etc.
In addition to this type of incendiary material, it was desirable to
have a spontaneously inflammable mixture of oils, which could be used
in Livens’ shell, Stokes’ shell or aeroplane bombs. The basis of these
mixtures is fuel oil and phosphorus. By varying the proportions of
the constituents it is possible to obtain a mixture that will ignite
immediately upon exposure to the air, or one that will have a delayed
action of from 30 seconds to two minutes.
The incorporation of metallic sodium gives a mixture that will ignite
when spread upon water surfaces.
INCENDIARY DEVICES
The incendiary devices used during the late war included: bombs, shell,
tracer shell and bullets, grenades, and flame throwers.
BOMBS
Incendiary bombs were used almost exclusively by aircraft. The value
of bombs which would cause destruction by starting conflagrations was
early recognized but their development was rather slow. While the
designs were constantly changing, two stand out as the most favored:
a small unit, such as the Baby Incendiary Bomb of the English, and a
large bomb, such as the French Chenard bomb or the American Mark II
bomb.
In general bombs which, when they function upon impact, scatter small
burning units over a considerable area, are not favored. Small unit
bombs can be more effectively used because the scatter can be better
regulated and the incendiary units can be more advantageously placed.
=German Bombs.= Incendiary bombs were used by the Germans in their
airplane raids, usually in connection with high explosive bombs. A
typical armament of the later series of German naval airships consisted
of the following:
2 660-pound bombs
10 220-pound bombs
15 110-pound bombs
20 Incendiary bombs
making a total weight of about 2½ tons.
[Illustration: FIG. 107.—Incendiary Devices.
(From Left to Right). Mark II Bomb, B. I. Bomb, Mark I Dart, Mark II
Dart, Mark I Dart, Grenade, Mark I Bomb.]
A typical German bomb is shown in Fig. 108. It consists essentially of
a receiver of white iron (R) composed of a casing and a central tube
of zinc, joined together in such a fashion that, when the whole was
complete, it had the appearance of an elongated vessel with a hollow
center. Within this central hollow is placed a priming tube (T) of thin
sheet iron, pierced by a number of circular openings. The receiver is
about 445 mm. (17.5 in.) high and 110 mm. (4.3 in.) at its maximum
diameter. It is wrapped with strands of tarred cord over nearly its
entire length. The empennage (270 mm. or 10.6 in.—in height) consisted
of three inclined balancing fins, which assured the rotation of the
projectile during its fall.
In the body of the bomb was a viscous mass of benzine hydrocarbons,
while the lower part of the receiver contained a mixture of potassium
perchlorate and paraffin. The central tube apparently contained a
mixture of aluminum and sulfur.
[Illustration: FIG. 108.—Aerial Incendiary Bomb, November, 1916.]
[Illustration: FIG. 109.—German Incendiary Bomb, Scatter Type.]
Later the Germans used a scatter type of bomb (Fig. 109) which was
designed to give 46 points of conflagration. Each of these 46 small
cylinders contained 50 grams of an air incendiary material. They were
arranged in layers, packed in with very fine gun powder. The bomb
is ignited by a friction lighter which is pulled automatically when
the bomb is released from the aeroplane. The bomb is constructed to
burst in the air and not on striking the ground. The upper part of the
projectile consists of a cast iron nose riveted to the sheet iron body
of the bomb. When the explosion occurs, the nose is blown away and the
small incendiary cylinders are scattered in the air.
The incendiary material appears to be a mixture of barium nitrate and
tar. Its incendiary power is very low because combustion takes the form
of a small flame of very short duration. It should, however, be very
valuable for firing inflammable materials.
=British Bombs.= The early British bombs were petrol bombs, which were
used without great success for crop burning. Phosphorus bombs were
then used for attacking aircraft. But the most successful incendiary
is the so-called “Baby Incendiary Bomb.” This is a 6.5-ounce bomb with
an incendiary charge of special thermit. These small bombs are carried
in containers holding either 144 or 272 bombs. The former container
approximates in size and weight one 50-pound H.E. bomb and the latter
one 120-pound H.E. bomb. The bomb contains a cartridge very much like a
shot gun shell which, on impact, sets down on the striker point in the
base of the body, and causes the ignition of the charge. It is claimed
that the cartridge of the B.I. bomb burns when totally immersed in any
liquid (water included) and in depths up to two feet the flame breaks
through the surface.
=French Bombs.= The French used three types of incendiary bombs, a
special thermit (calonite), the Chenard and the Davidsen. The Chenard
bomb is a true intensive type and is thought to be very successful.
It functions by means of a time fuse operated by the unscrewing of
a propeller, before striking the ground, and reaches its target in
flames. Its chief disadvantage is the small amount of incendiary
material which it carries. The Davidsen bomb expels its charge as a
single unit and is not considered as valuable or as successful as the
Chenard.
=American Bombs.= The program of the Chemical Warfare Service included
three types of bombs:
Mark II Incendiary drop bomb
Mark III Incendiary drop bomb
Mark I Scatter bomb
=Mark II Bomb.= The incendiary Mark II drop bomb is designed to be
dropped from an aeroplane and is intended for use against buildings,
etc., when penetrating effect followed by an intensive incendiary
action is sought.
The bomb case consists of two parts: a body and a nose. The body is a
tapering zinc shell which carries the firing mechanism and stabilizing
tail fin at the small end and at the large end a threaded ring which
screws into the nose. The nose is of drawn steel of such shape as to
have low end-on resistance and is sufficiently strong to penetrate
frame structures.
[Illustration: FIG. 110.—Loading Bombs with “Solid” Oil.]
The incendiary effect is produced by a thermit charge carried in the
nose of the bomb. This charge is ignited by a booster of “Thermit
Igniter” fired by black powder. The latter is ignited by a flash from
the discharge of a standard 0.30 caliber service cartridge contained in
the body of the bomb, and exploded by a firing mechanism of the impact
type. This method of firing has proven wholly unsatisfactory and will
be superseded by some more direct-acting mechanism. The body of the
bomb is filled with solidified oil. The molten thermit burns through
the case of the bomb and liberates the oil which has been partially
liquefied by the heat of the thermit reaction. Additional incendiary
effect is afforded by the sodium nitrate contained in the nose below
the thermit, and by two sheet lead cylinders filled with sodium and
imbedded in the solid oil. The sodium increases the difficulty of
extinguishing the fire with water.
=Mark III Bomb.= This bomb is simply a larger size of the Mark II bomb,
its weight being approximately 100 pounds as compared with 40 pounds
for the Mark II bomb. It is designed to be dropped from an aeroplane
and is intended for use against buildings when marked penetrating
effect is desired. The method of functioning is the same as the Mark II
bomb and it has the same defects in the firing mechanism.
=Mark I Bomb (Scatter Type).= The Mark I incendiary drop bomb is also
designed to be dropped from aeroplanes and is intended for use against
grain fields, ammunition dumps, light structures or similar objectives
when only a low degree of ignition is required. It is of the so-called
scatter type, due to the action of the exploding charge which casts
out incendiary material within a radius of 20 feet from the point of
contact.
The incendiary action is due to the ejection of the various incendiary
units in the bomb by the explosion of the black powder in the nose. The
flash of this explosion serves to ignite the units. A powder charge in
the rear of the bomb acts simultaneously with the nose charge, opening
the bomb casing, and aiding materially in the scatter of the units.
The bomb is so arranged as to function close to the ground, which is a
further factor in the scatter of the units.
The incendiary units are waste balls about 2.5 in. in diameter and
having an average weight of 2.5 ounces, tied securely with strong
twine. These are soaked in a special oil mixture. Carbon disulfide and
crude turpentine, or carbon disulfide, benzene heads and crude kerosene
gave satisfactory results. A later development attempted to replace
the waste balls by solid oil, but the difficulties of manufacture and
questions of transportation argued against its adoption.
These bombs were not used at the front. Nearly all of the American
incendiary bombs proved too light on the nose and lower half, generally
resulting in deformation upon impact and very poor results. New ones
will be made stronger.
INCENDIARY DARTS
The British early recognized the value of a small bomb, and
consequently adopted their B.I.B. (Baby Incendiary Bomb), weighing
about 6.5 ounces. These are capable of being dropped in lots of 100
or more and thus literally shower a given territory with fire. The
intensity of fire at any given point is much less than that obtained
with the larger bombs, but the increased area under bombardment more
than counter balances this disadvantage. While the British aimed at
the perfection of a universal bomb, the American service felt that two
classes should be developed, one to be used against grain fields and
forests, the other against buildings.
The first class was called the Mark I Dart. This consisted of an
elongated 12-gauge shot gun shell, filled with incendiary material
and provided with a firing mechanism to ignite the primer as the dart
strikes the ground. The flash of the primer sets fire to the booster,
which, in turn, ignites the main incendiary charge. The latter burns
several minutes, with a long flame. A retarding stabilizer attached
to the tail of the dart serves the two-fold purpose of insuring the
functioning of the firing mechanism and, by retarding the final
velocity of the dart, preventing the collapse of the dart body when
dropped from very high altitudes.
The incendiary mixture is one which gives a long hot flame, burns for
several minutes and leaves very little ash. In general it consists
of an oxidizing agent (barium or sodium chlorate), a reducing agent
(aluminum, or a mixture of iron, aluminum and magnesium), a filler
(rosin, powdered asphaltum or naphthalene) and in some cases a binder
(asphaltum, varnish or boiled linseed oil).
The Mark II Dart was developed to furnish a small size penetrating
agent. It consists of a two-inch (diameter) zinc case filled with
thermit and solid oil as the incendiary materials and provided with
a cast iron nose for penetration. During the first half minute after
firing, a pool of molten iron is formed by the thermit, which is very
penetrating and affords a good combustible surface for the oil, which
burns for an additional ten minutes.
It has an advantage over the Mark I dart in that it penetrates, and
over the Mark II bomb in that it is smaller and lighter in weight.
INCENDIARY SHELL
Incendiary shell have been successfully used against aircraft and
to some extent in bombardments of inflammable ground targets.
Anti-aircraft shell are of small caliber and are usually
tracer-incendiary. Such shell are filled with pyrotechnic mixtures
which ignite at the moment of firing, or by time fuse, and are
effective against highly inflammable material. Shell filled with
thermit which explode and scatter the molten iron have been used
against aircraft and ground targets, but with rather poor results.
Large shell, which burst upon impact and scatter units of burning
materials, have been used with some success against ground targets.
Tracer shell contain such mixtures as barium nitrate, magnesium and
shellac, or red lead and magnesium.
INCENDIARY BULLETS
Incendiary bullets are only effective against highly inflammable
material, and are therefore used principally in aerial warfare against
aircraft, either for the purpose of igniting the hydrogen of the gas
bag, or the gasoline. The present tendency is towards the use of the
large size (11 mm.) bullet, because of its greater incendiary action.
The incendiary material is either white phosphorus or a special
incendiary mixture consisting of an oxidizing agent and some
combustible or mixture of combustibles. The white tracer bullet
contains a mixture of barium peroxide and magnesium. A red bullet
contained in addition, strontium nitrate and chloride, or peroxide.
INCENDIARY HAND GRENADE
While the use of incendiary grenades and other small incendiary devices
is limited, such armament is considered very valuable in trench
warfare. They can be used to set fire to inflammable material, either
in offensive or defensive operations.
Phosphorus grenades, while used principally for producing smoke (see
page 302), have considerable value as an incendiary weapon.
Thermit grenades are very useful in rendering unserviceable guns
and other metallic equipment which must be abandoned. They permit
aviators to destroy planes which motor troubles oblige to land in enemy
territory. They are also used to ignite inflammable liquids, thrown
into a dugout, or sprayed over an objective by a flame projector.
The Mark I hand grenade was developed for burning enemy ammunition
dumps, for clearing away brush or other material in front of trenches
and for use in dugouts. The standard H.E. grenade body was half-filled
with thermit and half with a celluloid container filled with a
solidified fuel oil. The grenade is fired by the spit of the fuse of
the bouchon firing mechanism. This, through the booster, lights the
thermit igniter, which in turn fires the main charge of thermit. The
resulting molten iron readily penetrates the grenade case, at the same
time igniting the celluloid case and its contents. The oil burns for
about 3.5 minutes. This grenade was never used since it was considered
that an all thermit grenade would be of more value.
TRENCH MORTAR EQUIPMENT
Special projectiles were designed for use with the Stokes mortar and
the Livens’ projector. Thermit was used only in Stokes’ projectiles.
The Livens’ projectile was filled with inflammable units (chlorated
jute) immersed in a light oil mixture. Thrown from a projector into
the enemy’s trench, it explodes, giving a large flash and scattering
the burning units over an area of forty yards. The Mark II projectile,
designed for general incendiary effect against readily inflammable
material, consists of an altered 8-inch Livens’ gas projectile filled
with chlorated jute units impregnated with solid oil and immersed in
a spontaneously inflammable oil. After a short delay, these units
burst into flame and burn vigorously for several minutes. It is almost
impossible to extinguish them without large quantities of water. Such
bombs have only a very limited use, so that it is questionable if they
are really worth while.
[Illustration: FIG. 111.—German 8" Incendiary Bullet.]
[Illustration: FIG. 112.—German Incendiary Blue Pencil.]
GERMAN BLUE PENCIL
A very interesting and curious device was developed by the Germans in
the form of an incendiary pencil. Similar in appearance to a common
blue pencil, sharpened at one end, they are distinguished only by a
small, almost imperceptible, point placed on the outside 11 mm. from
the unsharpened end. They are 175 mm. long, 11.1 mm. in diameter and
weigh 12 to 13 grams. The interior of the pencil contains a glass
bulb, with two compartments filled with sulfuric acid and a celluloid
tube filled with potassium chlorate. The glass bulb ends in a slender
point; when this is broken the acid comes into contact with the
chlorate and causes an explosion. The two materials are separated by a
layer of clay, which causes a delayed action of about 30 minutes. The
operator breaks the point of bulb, buries the pencil vertically in the
inflammable material and then has half an hour in which to get away,
before any possibility of a fire. He cuts the pencil with a knife 2
cm. from the point, so that if caught he has the appearance of simply
sharpening a pencil.
FLAMING GUN
Among the unsuccessful weapons of the late war, the liquid fire gun
or Flammenwerfer, as the German called it, is probably the most
interesting. Its origin, according to a German story, was due to a
mere accident. A certain officer, during peace maneuvers, was ordered
to hold a fort at all cost. During the sham fight, having employed all
the means at his disposal, he finally called out the fire brigade and
directed streams of water upon the attacking force. Afterwards, during
the criticism of the operations in the presence of the Kaiser, he
claimed that he had subjected the attackers to streams of burning oil.
The Kaiser immediately inquired whether such a thing would be possible,
and was assured that it was entirely feasible.
[Illustration: Copyright by Kadel and Herbert, N. Y.
FIG. 113.—Liquid Fire Attack.]
Long series of experiments were necessary before a satisfactory
combination of oils was produced, which could be projected as a
flame on the enemy, but they were finally successful. Unlike the
use of poison gas, however, the flaming liquid gun did not prove to
be a successful weapon of warfare. True, at first they were rather
successful, but this was before the men learned their real nature. In
the first attack, the Allies were completely surprised and the troops
were routed by the flames. Auld tells of one of the early attacks (July
29, 1915) when, without warning, the front line troops were enveloped
in flames. Where the flames came from could not be seen. All that the
men knew was that they seemed surrounded by fierce, curling flames,
which were accompanied by a loud roaring noise, and dense clouds of
black smoke. Here and there a big blob of burning oil would fall into
a trench or saphead. Shouts and yells rent the air as individual men,
rising up in the trenches or attempting to move in the open, felt the
force of the flames. The only way to safety appeared to be to the rear.
This direction the men that were left took. For a short space the
flames pursued them and the local retirement became a local rout. After
the bombardment which followed, only one man is known to have returned.
After a study of the pictures of the liquid fire gun in operation, it
is evident that the men could not be blamed for this retirement. One
has only to imagine being faced by a spread of flame similar to that
used for the oil burners under the largest boiler, but with a jet
nearly 60 feet in length and capable of being sprayed round as one
might spray water with a fire hose.
Later, when the device was better known it was different, though even
then it was a pretty good test of a man’s nerve. It was found that
the flames could not follow one to the bottom of a trench as the gas
did, and that, if a man crouched to the bottom of his trench, his head
might be very warm for a minute or so but that the danger was soon past
and he then could pick off the man who had so recently made things
uncomfortable for him.
While it is said that Major R., who invented the Flammenwerfer, enjoyed
a great popularity among his men, and is familiarly known as the Prince
of Hades, there is no doubt that this was not shared by the Allies.
Their rule was: “Shoot the man carrying the apparatus before he gets
in his shot, if possible. If this cannot be done, take cover from the
flames and shoot him afterwards.”
The German had several types, which may be grouped into the _small_ or
_portable_ and the _large_ Flammenwerfers.
The portable Flammenwerfer consisted of a sheet steel cylinder of two
compartments, one to hold compressed nitrogen, the other to hold the
oil. The nitrogen furnished the pressure which forces the oil out
through the flexible tube. Air cannot be used, because the oxygen would
form an explosive mixture with the vapors of the oil, and any heating
on compression, or back flash from the flame or fuse might make things
very unpleasant for the operator. A pressure of about 23 atmospheres
is reached when the cylinder is charged. The nitrogen appeared to
be carried on the field in large containers and the flame projectors
actually charged in the trenches.
The oil used in the flame projectors varied from time to time, but
always contained a mixture of light or easily volatile and heavy and
less volatile fractions of petroleum or mineral oil, very carefully
mixed. In some cases even ordinary commercial ether has been found in
the cylinders.
[Illustration: FIG. 114.—Small Flammenwerfer.]
The most interesting part about the flame projector is the lighting
device. This is so made that the oil ignites spontaneously the minute
the jet is turned on, and is kept alight by a fiercely burning mixture
which lasts throughout the discharge. This mixture is composed of
barium nitrate, potassium nitrate, metallic magnesium and charcoal,
with some resinous material. The priming consists of black powder and
metallic magnesium.
When the oil rushes out of the jet, it forces up the plunger of a
friction lighter and ignites this core of fiercely burning mixture.
The range of these small projectors is from 14 to 17 meters (17 to 20
yards) but the duration of the flame is rather less than a minute.
In a later pattern, it was designed that one nozzle should be issued
to three reservoirs. After the discharge of one, the jet is attached
to the others in succession. This is called the “Wx” Flammenwerfer
(interchangeable). In this way a squad of three men could carry 58
pints of inflammable oil. It is a question, though, whether the third
man would live to use his reservoir.
[Illustration: FIG. 115.—Boyd Flame Projector.]
The fact that the trenches were often very close together during the
early part of the war, made possible the use of large or stationary
Flammenwerfer. These consisted of a steel reservoir 3⅓ feet in height
and 1⅔ feet in diameter, weighing about 250 pounds, which could be
connected to two steel cylinders, containing nitrogen under pressure.
These carried 180 liters (40 gallons) of liquid and operated under a
pressure of 15 atmospheres. The discharge nozzle was at the end of a
metal tube three feet long, and its orifice was about ⁵/₁₆ of an inch
in diameter. The range of this apparatus was from 33 to 40 yards and
the duration of the flame from one to two minutes. Because of the
comparatively short range of these guns and the ease with which they
could be destroyed, if located by the enemy, their use was very limited.
Even with the portable flammenwerfer, the most difficult thing to do
is to get near enough the target to make the shoot effective. Another
serious disadvantage is its very short duration. It is impossible to
charge up again on the spot, and the result is that once the flame
stops, the whole game is finished and the operators are at the mercy of
the enemy.
With these facts in mind it is easy to see how service in the flaming
gun regiments is apparently a form of punishment. Men convicted of
offenses in other regiments were transferred either for a time or
permanently and were forced under threat of death in the most hazardous
enterprises and to carry out the most dangerous work. Taken all in
all the flame thrower was one of the greatest failures among the many
promising devices tried out on a large scale in the war.