The stern test of war has served to reveal conclusively the fact that
aerial craft can be put out of action readily and effectively, when once
the marksman has picked up the range, whether the gunner be conducting
his operations with an anti-aircraft gun stationed upon the ground,
or from a hostile machine. It will be remembered that Flight-Commander
Briggs, on the occasion of the daring British raid upon the Zeppelin
sheds at Friedrichshafen, was brought to the ground by a bullet which
penetrated his fuel tank. Several other vessels, British, German,
French, and Russian alike, have been thrown out of action in a similar
manner, and invariably the craft which has been disabled suddenly in
this way has fallen precipitately to earth in the fatal headlong dive.
Previous to the outbreak of hostilities there was considerable
divergence of opinion upon this subject. The general opinion was that
the outspread wings and the stays which constituted the weakest parts of
the structure were most susceptible to gun-fire, and thus were likely to
fail. But practice has proved that it is the driving mechanism which is
the most vulnerable part of the aeroplane.
This vulnerability of the essential feature of the flying machine is a
decisive weakness, and exposes the aviator to a constant menace. It
may be quite true that less than one bullet in a thousand may hit the
machine, but when the lucky missile does find its billet its effect is
complete. The fact must not be overlooked that the gunners who work the
batteries of anti-aircraft guns are becoming more and more expert as a
result of practice, so that as time progresses and improved guns for
such duty are rendered available, the work of the aviator is likely to
become more dangerous and difficult. Experience has proved that the high
velocity gun of to-day is able to hurl its projectile or shell to an
extreme height--far greater than was previously considered possible--so
that considerable discretion has to be exercised by the airman, who
literally bears his life in his hands.
Although elaborate trials were carried out upon the testing ranges with
the weapons devised especially for firing upon flying machines, captive
balloons being employed as targets, the data thus obtained were neither
conclusive nor illuminating. The actual experiences of airmen have given
us some very instructive facts upon this point for the first time.
It was formerly held that the zone of fire that is to be considered as
a serious danger was within a height of about 4,500 feet. But this
estimate was well within the mark. Airmen have found that the modern
projectiles devised for this phase of operations are able to inflict
distinctly serious damage at an altitude of 9,000 feet. The shell itself
may have but little of its imparted velocity remaining at this altitude,
but it must be remembered that when the missile bursts, the contents
thereof are given an independent velocity, and a wide cone of
dispersion, which is quite sufficient to achieve the desired end,
inasmuch as the mechanism of the modern aeroplane and dirigible is
somewhat delicate.
It was for this reason that the possibility of armouring the airship was
discussed seriously, and many interesting experiments in this field were
carried out. At the same time it was decided that the armouring
should be effected upon lines analogous to that prevailing in warship
engineering. The craft should not only be provided with defensive but
also with aggressive armament. This decision was not viewed with general
approbation. It was pointed out that questions of weight would arise,
especially in relation to the speed of the machine. Increased weight,
unless it were accompanied by a proportionate augmentation of power
in the motor, would react against the efficiency and utility of the
machine, would appreciably reduce its speed, and would affect its
climbing powers very adversely. In some quarters it was maintained
that as a result the machine would even prove unsuited to military
operations, inasmuch as high speed is the primary factor in these.
Consequently it was decided by the foremost aviating experts that
machines would have to be classified and allotted to particular spheres
of work, just as warships are built in accordance with the special
duty which they are expected to perform. In reconnaissance, speed is
imperative, because such work in the air coincides with that of
the torpedo-boat or scout upon the seas. It is designed to acquire
information respecting the movements of the enemy, so as to assist the
heavier arms in the plan of campaign. On the other hand, the fighting
corsair of the skies might be likened to the cruiser or battleship. It
need not possess such a high turn of speed, but must be equipped with
hard-hitting powers and be protected against attacking fire.
One attempt to secure the adequate protection against gun-fire from the
ground assumed the installation of bullet-proof steel plating, about one
fifth of an inch thick, below the tank and the motor respectively.
The disposition of the plating was such as to offer the minimum of
resistance to the air and yet to present a plane surface to the ground
below. So far as it went this protection was completely effective, but
it failed to armour the vital parts against lateral, cross and downward
fire while aloft. As the latter is more to be feared than the fire from
the ground, seeing that it may be directed at point blank range, this
was a decided defect and the armour was subsequently abandoned as
useless.
The only effective method of achieving the desired end is to armour the
whole of the carriage or fuselage of the adroplane, and this was the
principle adopted by the Vickers Company. The Vickers military aeroplane
is essentially a military machine. It is built of steel throughout.
The skeleton of the machine is formed of an alloy which combines the
qualities of aluminium and steel to ensure toughness, strength, and
lightness. In fact, metal is employed liberally throughout, except in
connection with the wings, which follow the usual lines of construction.
The body of the car is sheathed with steel plating which is bullet proof
against rifle or even shrapnel fire. The car is designed to carry two
persons; the seats are therefore disposed tandem-wise, with the observer
or gunner occupying the front seat.
The defensive armament is adequate for ordinary purposes. Being fitted
with a 100 horse-power motor, fairly high speeds are attainable,
although the velocity is not equal to that of machines constructed upon
conventional lines, inasmuch as there is an appreciable increase in
weight.
The car is short and designed upon excellent stream lines, so that the
minimum of resistance to the air is offered, while at the same time the
balancing is perfect. The sides of the car are brought up high enough
to protect the aviators, only their heads being visible when they are
seated. The prow of the car follows the lines generally adopted in high
speed torpedo boat design; there is a sharp knife edge stem with an
enclosed fo'c's'le, the latter housing the gun.
Another craft, designed for scouting operations, may be likened to
the mosquito craft of the seas. This machine, while a biplane like
the military aeroplane, is of lighter construction, everything
being sacrificed to speed in this instance. It is fitted with a 100
horse-power motor and is designed to carry an observer if required.
There is no offensive armament, however. The fuel tank capacity,
moreover, is limited, being only sufficient for a two or three hours'
flight. While this is adequate for general reconnoitring, which for the
most part entails short high speed flights, there are occasions when
the Staff demands more prolonged observations conducted over a greater
radius. This requisition can be met by eliminating the observer, whose
duties in this instance must be assumed by the pilot, and substituting
in place of the former, a second fuel tank of sufficient capacity for a
flight of four or five hours, thereby bringing the term of action in the
air to about 6 1/4 hours. This machine travels at a very high speed and
is eminently adapted to its specific duty, but it is of limited service
for general purposes.
The arming of an aeroplane, to enable it to defend itself against
hostile attack or to participate in raiding operations upon the aerial
fleet of the enemy, appears to be a simple task, but as a matter of
fact it is an undertaking beset with difficulties innumerable. This is
especially the case where the aeroplane is of the tractive type, that is
to say where the propellers are placed in the forefront of the machine
and in their revolution serve to draw the machine forward. All other
considerations must necessarily be sacrificed to the mounting of the
propeller. Consequently it is by no means easy to allot a position for
the installation of a gun, or if such should be found there is grave
risk of the angle of fire being severely restricted. In fact, in many
instances the mounting of a gun is out of the question: it becomes a
greater menace to the machine than to the enemy.
The French aeronautical section of the military department devoted
considerable study to this subject, but found the problem almost
insurmount able. Monsieur Loiseau met with the greatest measure of
success, and his system is being practised in the present campaign. This
principle is essentially adapted to tractor aeroplanes. Forward of the
pilot a special position is reserved for the gunner. A special mounting
is provided towards the prow, and upon the upper face of the body of the
machine. The gun mounting is disposed in such a manner that it is able
to command a wide arc of fire in the vertical plane over the nose of the
machine and more particularly in the downward direction.
The marksman is provided with a special seat, but when he comes into
action he has to stand to manipulate his weapon. The lower part of his
body is protected by a front shield of steel plate, a fifth of an inch
in thickness, while a light railing extending upon either side and
behind enables the gunner to maintain his position when the aeroplane is
banking and climbing. The machine gun, of the Hotchkiss type, is mounted
upon a swivel attached to a tripod, while the latter is built into the
bracing of the car, so as to ensure a fairly steady gun platform.
While the gun in the hands of a trained marksman may be manipulated with
destructive effect, the drawbacks to the arrangement are obvious. The
gunner occupies a very exposed position, and, although the bullet-proof
shield serves to break the effects of wind when travelling at high
speed which renders the sighting and training of the weapon extremely
difficult, yet he offers a conspicuous target, more particularly when
the enemy is able to assume the upper position in the air as a result of
superior speed in travelling. The gun, however, may be elevated to about
60 degrees, which elevation may be accentuated by the inclination of the
aeroplane when climbing, while the facility with which the weapon may be
moved through the horizontal plane is distinctly favourable.
But the aerial marksman suffers from one very pronounced defect: he has
a severely restricted survey of everything below, since his vision is
interrupted by the planes. The result is that an enemy who has lost
ascendancy of position is comparatively safe if he is able to fly
immediately below his adversary: the mitrailleuse of the latter cannot
be trained upon him. On the other hand the enemy, if equipped with
repeating rifles or automatic pistols, is able to inflict appreciable
damage upon the craft overhead, the difficulties of firing vertically
into the air notwithstanding.
In the Vickers system, where the propeller is mounted behind the car,
the aeroplane thus operating upon the pusher principle, the nose of the
car is occupied by the arm, which is a rifle calibre machine gun fitted
upon a special mounting. The prow is provided with an embrasure for
the weapon and the latter is so installed as to command an angle of 30
degrees on all sides of the longitudinal axis of the machine when
in flight. In this instance the marksman is provided with complete
protection on all sides, inasmuch as his position is in the prow, where
the hood of the fo'c's'le shields him from overhead attack. The gun
is protected by a special shield which moves with the gun barrel. This
shield is provided with mica windows, through which the gunner is able
to sight his arm, so that he is not inconvenienced in any way by the
wind draught.
One shortcoming of such methods of arming an aeroplane will be observed.
Ahead firing only is possible; the weapon cannot be trained astern,
while similarly the line of fire on either broadside is severely
limited. This is one reason why the machine-gun armament of aerial craft
of the heavier-than-air type has not undergone extensive development.
In many instances the pilot and observer have expressed their preference
for repeating high velocity rifles over any form of fixed gun mounting,
and have recourse to the latter only when the conditions are extremely
favourable to its effective employment.
Efforts are now being made to equip the military type of aeroplane with
both forward and astern firing guns. The urgency of astern fire has
been brought home very vividly. Suppose, for instance, two hostile
aeroplanes, A and B, are in the air. A has the advantage at first, but
B is speedier and rapidly overhauls A. During the whole period of the
overhauling movement the gun of B can be directed upon A, while the
latter, owing to the arc of training being limited to c d cannot reply.
Obviously in the running fight it would be to the advantage of B,
although the fleeter machine, to keep behind A (position 1), but the
latter is making towards its own lines.
Under these circumstances A must be headed off, so B crowds on speed
to consummate this end. But in the overtaking process B renders his
gun-fire ineffective, inasmuch as B passes beyond the arc of his gun
which is represented by e f. But in so doing B comes within the firing
arc of A (position 9). To minimise this danger B ascends to a higher
level to obtain the paramount position.
If, however, B were equipped with an astern gun the aeroplane A would
be within the fire of B when the forward gun of the latter could not
be used. Similarly if A were also fitted with an astern gun it would be
able to attack its pursuer the whole time B was to its rear and in
this event, if its gun-fire were superior, it would be able to keep
the latter to a safe distance, or compel B to manoeuvre into a superior
position, which would entail a certain loss of time.
An astern firing gun would be valuable to B in another sense. Directly
it had passed A or brought the latter within the zone of its astern gun
it could maintain its fire at the most advantageous range, because owing
to its speed it would be able to dictate the distance over which shots
should be exchanged and if mounted with a superior weapon would be able
to keep beyond the range of A's guns while at the same time it would
keep A within range of its own gun and consequently rake the latter. In
the interests of self-preservation A would be compelled to change
its course; in fact, B would be able to drive it in any direction he
desired, as he would command A's movements by gun-fire.
The value of combined ahead and astern firing has been appreciated, but
there is one difficulty which at the moment appears to be insuperable
the clearance of the propeller. At the moment astern-firing, if such it
may be called, is maintained by repeating rifles, but this armament
is not to be compared with machine-gun firing, as the latter with
its capacity to pour 400 to 600 shots a minute, is far more deadly,
particularly when the weapon is manipulated by a crack gunner.
Up to the present the offensive armament of aeroplanes has been confined
to light machine guns such as the Hotchkiss, Berthier, Schwartlose,
and Maxim weapons. So far as the arming of aeroplanes is concerned the
indispensable condition is light weight. With airships this factor is
not so vital, the result being that some dirigibles are mounted with
guns, throwing one pound bursting shells, fitted either with delay
action or percussion fuses, the former for preference. These shells are
given a wide cone of dispersion. Experiments are also being made with a
gun similar to the pom-pom which proved so useful in South Africa, the
gun throwing small shells varying from four to eight ounces in weight at
high velocity and in rapid succession. While such missiles would not be
likely to inflict appreciable damage upon an armoured aeroplane, they
would nevertheless be disconcerting to the aviators subjected to
such fire, and in aerial combats the successful undermining of the
adversary's moral is of far greater importance than in land operations,
since immediately ascendancy in the artillery operations is attained the
final issue is a matter of moments.
But the most devastating arm which has yet been contrived for aerial
operations is the light machine gun which has recently been perfected.
The one objective with this weapon is to disable the hostile aircraft's
machinery. It fires an armour piercing projectile which, striking the
motor of any aircraft, would instantly put the latter out of action. The
shell has a diameter of about.75 inch and weighs about four ounces. The
gun is a hybrid of the mitrailleuse and the French "Soixante-quinze,"
combining the firing rapidity of the former with the recoil mechanism
of the latter. This missile has established its ability to penetrate
the defensive armouring of any aeroplane and the motor of the machine
at 1,000 yards' range. This offensive arm is now being manufactured, so
that it is likely to be seen in the near future as the main armament of
aeroplanes.
At the moment widespread efforts are being made in the direction of
increasing the offensive efficiency of aircraft. It is one of the phases
of ingenuity which has been stimulated into activity as a result of the
war.