When the airship and the aeroplane became accepted units of warfare it
was only natural that efforts should be concentrated upon the evolution
of ways and means to compass their destruction or, at least, to restrict
their field of activity. But aircraft appeared to have an immense
advantage in combat. They possess virtually unlimited space in which to
manoeuvre, and are able to select the elevation from which to hurl their
missiles of destruction.
There is another and even more important factor in their favour. A
projectile fired, or even dropped, from a height, say of 5,000 feet,
is favourably affected by the force of gravity, with the result that
it travels towards the earth with accumulating energy and strikes the
ground with decisive force.
On the other hand, a missile discharged into space from a weapon on the
earth has to combat this action of gravity, which exercises a powerful
nullifying influence upon its flight and velocity, far in excess of
the mere resistance offered by the air. In other words, whereas the
projectile launched from aloft has the downward pull of the earth or
gravitational force in its favour, the shell fired from the ground in
the reverse direction has to contend against this downward pull and its
decelerating effect.
At the time when aircraft entered the realms of warfare very little
was known concerning the altitudes to which projectiles could be
hurled deliberately. Certain conclusive information upon this point was
available in connection with heavy howitzer fire, based on calculations
of the respective angles at which the projectile rose into the air and
fell to the ground, and of the time the missile took to complete its
flight from the gun to the objective. But howitzer fire against aircraft
was a sheer impossibility: it was like using a six-inch gun to kill a
fly on a window pane at a thousand yards' range. Some years ago
certain experiments in aerial firing with a rifle were undertaken
in Switzerland. The weapon was set vertically muzzle upwards and
discharged. From the time which elapsed between the issue of the bullet
from the muzzle until it struck the earth it was possible to make
certain deductions, from which it was estimated that the bullet reached
an altitude of 600 feet or so. But this was merely conjecture.
Consequently when artillerists entered upon the study of fighting
air-craft with small arms and light guns, they were compelled to
struggle in the dark to a very pronounced extent, and this darkness was
never satisfactorily dispelled until the present war, for the simple
reason that there were no means of getting conclusive information. The
German armament manufacturers endeavoured to solve the problem by using
smoking shells or missiles fitted with what are known as tracers. By
following the ascensional path of the projectiles as revealed by the
smoke it was possible to draw certain conclusions. But these were by no
means convincing or illuminating, as so many factors affected the issue.
Despite the peculiar and complex difficulties associated with the
problem it was attacked some what boldly. In this trying field of
artillery research the prominent German armament manufacturers, Krupp
of Essen and Ehrhardt of Dusseldorf, played a leading part, the result
being that before the airship or the aeroplane was received within the
military fold, the anti-aircraft gun had been brought into the field
of applied science. The sudden levelling-up serves to illustrate the
enterprise of the Germans in this respect as well as their perspicacity
in connection with the military value of aircraft.
Any gun we can hope to employ against aircraft with some degree of
success must fulfil special conditions, for it has to deal with a
difficult and elusive foe. Both the lighter-than-air and the heavier
than-air craft possess distinctive features and varying degrees of
mobility. Taking the first-named, the facility with which it can vary
its altitude is a disconcerting factor, and is perplexing to the most
skilful gunner, inasmuch as he is called upon to judge and change the
range suddenly.
On the other hand, the artilleryman is favoured in certain directions.
The range of utility of the airship is severely limited. If its avowed
mission is reconnaissance and conclusive information concerning the
disposition of forces, artillery and so forth is required, experience
has proved that such work cannot be carried out satisfactorily or with
any degree of accuracy at a height exceeding 5,000 feet, and a distance
beyond six miles. But even under these circumstances the climatic
conditions must be extremely favourable. If the elements are
unpropitious the airship must venture nearer to its objective. These
data were not difficult to collect, inasmuch as they were more or
less available from the results of military observations with captive
balloons, the conditions being somewhat similar. With the ordinary
captive balloon it has been found that, in clear weather, a radius of
about 3 3/4 miles at the maximum elevation constitutes its range of
reliable utility.
With the aeroplane, however, the conditions are very dissimilar. In the
first place the machine owing to its diminutive size as compared with
the airship, offers a small and inconspicuous target. Then there is
its high independent speed, which is far beyond that of the airship.
Furthermore its mobility is greater. It can wheel, turn sharply to the
right or to the left, and pursue an irregular undulating flight in the
horizontal plane, which renders it well nigh impossible for a gunner to
pick it up. The machine moves at a higher relative speed than that at
which the gun can be trained. It is the rapid and devious variation
which so baffles the gunner, who unless he be highly skilled and
patient, is apt to commence to fire wildly after striving for a few
moments, and in vain, to pick up the range; he trusts to luck or depends
upon blind-shooting, which invariably results in a waste of ammunition.
A gun, to be of tangible destructive efficiency when directed against
aircraft, especially those depending upon the gas-bag for equilibrium,
must be of special design. It must be capable of firing at an angle only
a few degrees less than the absolute vertical, and in order to follow
the rapid and involved movements of its objective, must be so mobile
that it can be trained through a complete circle at any angle of
inclination less than its maximum. At the same time, if the weapon is
being used in field operations it must be mounted upon a carriage of
adequate mobility to enable it to follow the airship, and thereby keep
pace with the latter, so that the aerial craft may be sorely harassed if
not actually hit. The automobile is the obvious vehicle for this duty,
and it has accordingly been extensively used in this service.
The automobile and the gun mounted thereon follow widely different
lines. Some vehicles are designed especially for this duty, while others
are improvisations, and be it noted, in passing, that many of the latter
have proved more serviceable than the former. Still, the first-named
is to be preferred, inasmuch as necessarily it is designed to meet the
all-round requirements imposed, and consequently is better able to
stand up to the intended work, whereas the extemporised vehicle is only
serviceable under favourable conditions.
The Krupp Company has evolved many designs of anti-aircraft motor-driven
guns--"Archibalds" the British airmen term them with emphatic levity.
They are sturdily-built vehicles fitted with heavy motors, developing
from 40 to 50 horse-power, with the chassis not widely dissimilar from
that adopted for motor-omnibus traffic. Consequently, they are not
necessarily condemned to the high-roads, but within certain limits
are able to travel across country, i.e., upon fields or other level
expanses, where the soil is not unduly soft.
But the very character of the problem rendered the evolution of the
vehicle a somewhat perplexing matter. There were many factors which had
to be taken into consideration, and it was possible to meet the imposed
requirements only within certain limits. In the first place, the weight
of the gun itself had to be kept down. It was obviously useless to
overload the chassis. Again, the weight of the projectile and its
velocity had to be borne in mind. A high velocity was imperative.
Accordingly, an initial velocity varying from 2,200 to 2,700 feet per
second, according to the calibre of the gun, was determined.
Moreover, as mobility was an indispensable condition, the gun had to be
so mounted that it could be fired from the motor-car even if the
latter were travelling at high speed. This requirement entailed another
difficulty. The gun had to be mounted in such a manner as to enable the
gunner to train it easily and readily through the complete circle and
through its complete range of vertical inclination. As the result
of prolonged experiments it was ascertained that the most suitable
arrangement was a pedestal mounting, either within a turret or upon an
open deck. To meet the weight of the gun, as well as the strains and
stresses incidental to firing, the chassis was strengthened, especially
over the rear axle near which the mounting is placed.
The heaviest gun of this type is the 10.5 centimetre (4 1/4-inch)
quick-firer, throwing a shell weighing nearly forty pounds, with an
initial velocity of 2,333 feet per second. This "Archibald" is totally
unprotected. The gun is mounted centrally upon the carriage over the
rear axle, and occupies the centre of the deck between the driver's seat
and that of the gun crew behind. The whole of the deck is clear, thereby
offering no obstruction to the gunner in training the weapon, while the
space may be widened by dropping down the wings of the vehicle. At the
rear is a seat to accommodate the gun crew, beneath which the ammunition
is stowed. When travelling and out of action, the gun lies horizontally,
the muzzle pointing from the rear of the car.
To reduce the strains arising from firing, the arm is fitted with
what is known as the "differential recoil." Above the breach is an air
recuperator and a piston, while there is no hydraulic brake such as is
generally used. The compressor is kept under compression while the car
is travelling with the gun out of action, so that the arm is available
for instant firing. This is a departure from the general practice in
connection with such weapons. When the gun is loaded the bolt which
holds the compressor back is withdrawn, either by the hand for manual
firing, or by the action of the automatic closing of the breech when the
arm is being used as a quick-firer. In firing the gun is thrown forward
under the pressure of the released air which occurs at the moment of
discharge. The energy of the recoil brings the gun back and at the same
time recharges the compressed air reservoir.
The gun is so mounted upon its pedestal as to enable a maximum vertical
inclination of 75 degrees to be obtained. The mounting system also
enables the weapon to be trained in any desired direction up to the
foregoing maximum elevation throughout a complete circle, and it can
be handled with ease and celerity. A smaller "Archibald" is the 7.5
centimetre (3-inch gun) throwing a 14.3 pound shell at an initial
velocity of about 2,170 feet per second.
The turret anti-aircraft gun carried upon a motor-car differs from the
foregoing very considerably. This is a protected arm. The gun of 7.1
centimetres--approximately 2.75 inches--is mounted in the same manner
upon the car-deck and over the driving axle, but is enclosed within a
sheet steel turret, which is proof against rifle and machine-gun
fire. This turret resembles the conning-tower of a battleship, and is
sufficiently spacious to house the whole of the gun crew, the internal
diameter being about seven feet. Access to the turret is obtained
through a rear door. This gun has a maximum elevation of about 75
degrees, while its operation and mechanism are similar to those of the
unprotected weapon.
The vehicle itself is practically identical with the armoured motor-car,
which has played such an important part during the present campaign, the
driver being protected by a bullet-proof steel screen similar in design
to the ordinary glass wind-screen fitted to touring automobiles. This is
carried sufficiently high to offer complete protection to his head when
seated at the wheel, while through a small orifice in this shield he is
able to obtain a clear view of the road. The engine and its vital
parts are also adequately protected. The ammunition is carried in a
cupboard-like recess forming part of the driver's seat, encased in
bullet-proof steel sheeting with flap-doors. This device enables the
shells to be withdrawn readily from the side of the car and passed to
the crew within the turret. The caisson is of sufficient dimensions to
receive 69 shells.
The Ehrhardt airship fighting ordnance is similarly adapted to motor-car
operations, one type being especially powerful. The whole of the vehicle
is encased in armour-plating impervious to rifle and machine-gun fire.
The driver is provided with a small orifice through which he is able to
obtain a clear uninterrupted view of the road ahead, while the armouring
over the tonneau is carried to a sufficient height to allow head-room to
the gun crew when standing at the gun. All four wheels are of the disk
type and fashioned from heavy sheet steel. The motor develops 40-50
horse-power and, in one type, in order to mitigate the risk of
breakdown or disablement, all four wheels are driven. The gun, a small
quick-firer, is mounted on a pedestal in a projecting conning-tower. The
mounting is placed behind the driver's seat, and is trained and operated
from the tonneau. The maximum elevation is 75 degrees, and like the
gun carriage bearing the tube guide it can be moved through a complete
circle, being free to rotate in the fixed pivot jack to enable this end
to be attained.
The foregoing may be said to represent the most powerful types of mobile
anti-aircraft weapons used by the Austro-German forces to-day. Arms of
similar design, roughly speaking, have also been introduced into the
French and Russian services. In addition many semi-armoured weapons
of this character are in operation, some specially built for the work,
while others have been improvised. In the semi-armoured motor-car the
carriage follows the usual lines; it has an open top, the armouring
comprising the body of the tonneau and the diskwheels, which are made of
light bullet-proof steel. Here again the prevailing practice is to mount
the gun as nearly above the rear axle as possible, and to work it from
the tonneau. The maximum elevation is also 75 degrees, with training
throughout the entire circle.
Another type comprises a very light machine gun of rifle calibre, and
this is intended for attachment to an ordinary motor car. There is a
pedestal mounting which can be set within the tonneau, while the weapon
is pivoted in an outrigger, the latter being free to rotate in its pivot
jack. This arrangement enables the arm to cover a wide range, while it
also admits of training through an extensive angle of elevation.
The Allied forces improvised travelling anti-aircraft offences by
mounting the latest types of Vickers, Hotchkiss, and other machine guns
in armoured motor cars. Some of these have the domed turret form, with
the gun projecting through the roof, while others are protected against
hostile attack from the side only, the carriage being panelled with
bullet-proof steel sheeting. While such weapons are useful, inasmuch as
they can maintain a hot fire ranging up to 750 shots per minute, they
are not to be compared with the "Archibalds," which are able to throw
heavy shrapnel and incendiary shells, and have a vertical range of about
6,000 to 8,000 feet.
The improvised motor-gun has not proved a complete success, except
in those instances when the hostile aircraft has ventured to approach
somewhat closely to the ground. The more formidable weapons cannot be
mounted upon ordinary vehicles, inasmuch as the increase in weight,
which is appreciable, impairs the efficiency of the vehicle, and at the
same time enhances the possibility of breakdown at a critical moment.
For such arms a special and substantial chassis is imperative, while the
motive power and gearing must be adapted to the circumstances.
Motor-mounted anti-aircraft weapons, however, have not proved an
unqualified success. The fact that the vehicles are condemned to the
high roads, or at least to comparatively smooth and level ground,
constitutes a severe handicap. Again, when travelling at high speed, and
this is essential when pursuing a fast aeroplane, the accurate laying
of the weapon is extremely difficult, owing to the oscillation of the
vehicle itself, especially if the road surface is in a bad condition.
The sighting arrangements are of a wonderfully complete character, as
described elsewhere, but the irregular rolling movement arising from
high speed is a nullifying quantity. It is tolerably easy for the
aircraft, especially an aeroplane, to evade successful pursuit, either
by rising to an elevation beyond the range of the gun, or by carrying
out baffling evolutions such as irregular undulating flight, wheeling,
and climbing. According to the reports of the British and French airmen
the "Archibald" has failed to establish the glowing reputation which was
anticipated, for the simple reason that, unless it has a clear straight
road and can maintain its high speed, it can easily be out-distanced by
the fleet human bird.
The motor-car suffers from another serious disability. It cannot
manoeuvre with sufficient celerity. For instance, if it is necessary to
turn round in a narrow lane, valuable time is lost in the process, and
this the airman turns to account. In hilly country it is at a still
greater disadvantage, the inclines, gradients, and sinuosities of the
roads restricting its effectiveness very pronouncedly. It must also be
remembered that, relatively speaking, the "Archibald" offers a better
target to the airman than the aeroplane offers to the man behind the
anti-aircraft gun on the motor below. A few well-placed bombs are
sufficient to induce the pursuers to cease their activities. Even if the
missiles fail to strike the motor-car itself they can wreak disaster in
directly by rendering the road impassable or dangerous to negotiate
at high speed. On the whole therefore, the "Archibald" is a greatly
exaggerated weapon of offence against aircraft, and, so far as is known,
has failed to fulfil expectations. In fact, the Germans have practically
abandoned the idea of using it in the manner of a pursuing arm; they
work the weapon as a fixture, depending upon the car merely as a
means of moving it from point to point. Thus, in reality, it has been
converted into a light field-piece, and may almost be included in the
category of fixed weapons for combating aerial operations.