Although the captive balloon is recognised as indispensable in military
operations, its uses are somewhat limited. It can be employed only in
comparatively still weather. The reason is obvious. It is essential that
the balloon should assume a vertical line in relation to its winding
plant upon the ground beneath, so that it may attain the maximum
elevation possible: in other words, the balloon should be directly
above the station below, so that if 100 yards of cable are paid out the
aerostat may be 100 yards above the ground. If a wind is blowing, the
helpless craft is certain to be caught thereby and driven forwards or
backwards, so that it assumes an angle to its station. If this become
acute the vessel will be tilted, rendering the position of the observers
somewhat precarious, and at the same time observing efficiency will be
impaired.
This point may be appreciated more easily by reference to the
accompanying diagram. A represents the ground station and B the position
of the captive balloon when sent aloft in calm weather, 300 feet of
cable being paid out. A wind arises and blows the vessel forward to the
position C. At this point the height of the craft in relation to the
ground has been reduced, and the reduction must increase proportionately
as the strength of the wind increases and forces the balloon still more
towards the ground. At the same time, owing to the tilt given to the
car, observation is rendered more difficult and eventually becomes
extremely dangerous.
A wind, if of appreciable strength, develops another and graver danger.
Greater strain will be imposed upon the cable, while if the wind be
gusty, there is the risk that the vessel will be torn away from
its anchoring rope and possibly lost. Thus it will be seen that the
effective utilisation of a captive balloon is completely governed by
meteorological conditions, and often it is impossible to use it
in weather which exercises but little influence upon dirigibles or
aeroplanes.
The captive balloon equipment comprises the balloon, together with the
observer's basket, the wire-cable whereby it is anchored and controlled,
and the winding apparatus. Formerly a steam engine was necessary for
the paying in and out of the cable, but nowadays this is accomplished by
means of a petrol-driven motor, an oil-engine, or even by the engine of
an automobile. The length of cable varies according to the capacity of
the balloon and the maximum operating height.
The average British balloon is able to lift about 290 or 300 pounds,
which may be taken to represent the weight of two observers. On the
other hand, the French and German balloons are able to carry four times
this weight, with the exception of the French auxiliaries, which are
designed to lift one observer only. The balloons of the two latter
Powers have also a greater maximum altitude; it is possible to ascend to
a height of some 2,000 feet in one of these.
The observing station is connected with the winding crew below either
by a telephone, or some other signalling system, the method practised
varying according to circumstances. In turn the winding station is
connected with the officer in charge of the artillery, the fire of which
the captive balloon is directing. The balloon observer is generally
equipped with various instruments, such as telescope, photographic
cameras, and so forth, so as to be able, if necessary, to prepare a
topographical survey of the country below. By this means the absence
of reliable maps may be remedied, or if not regarded, as sufficiently
correct they may be checked and counter-checked by the data gained
aloft.
Seeing that the gas has to be transported in cylinders, which are
weighty, it is incumbent that the waste of this commodity should be
reduced to the minimum. The balloon cannot be deflated at night and
re-inflated in the morning--it must be maintained in the inflated
condition the whole time it is required for operation.
There are various methods of consummating this end. One method is to
haul in the balloon and to peg it down on all sides, completing the
anchorage by the attachment of bags filled with earth to the network.
While this process is satisfactory in calm weather, it is impracticable
in heavy winds, which are likely to spring up suddenly. Consequently
a second method is practised. This is to dig a pit into the ground of
sufficient size to receive the balloon. When the latter is hauled in it
is lowered into this pit and there pegged down and anchored. Thus it
is perfectly safe during the roughest weather, as none of its bulk is
exposed above the ground level. Furthermore it is not a conspicuous
object for the concentration of hostile fire.
In some instances, and where the military department is possessed of
an elaborate equipment such as characterises the German army, when
reconnaissance is completed and the balloon is to be removed to another
point, the gas is pumped back into the cylinders for further use. Such
an economical proceeding is pretty and well adapted to manoeuvres, but
it is scarcely feasible in actual warfare, for the simple reason that
the pumping takes time. Consequently the general procedure, when the
balloon has completed its work, is to permit the gas to escape into the
air in the usual manner, and to draw a fresh supply of gas from further
cylinders when the occasion arises for re-inflation.
Although the familiar spherical balloon has proved perfectly adequate
for reconnoitring in the British and French armies, the German
authorities maintained that it was not satisfactory in anything but calm
weather. Accordingly scientific initiative was stimulated with a view to
the evolution of a superior vessel. These endeavours culminated in the
Parseval-Siegsfeld captive balloon, which has a quaint appearance. It
has the form of a bulky cylinder with hemispherical extremities. At one
end of the balloon there is a surrounding outer bag, reminiscent of a
cancerous growth. The lower end of this is open. This attachment serves
the purpose of a ballonet. The wind blowing against the opening, which
faces it, charges the ballonet with air. This action, it is claimed,
serves to steady the main vessel, somewhat in the manner of the tail of
a kite, thereby enabling observations to be made as easily and correctly
in rough as in calm weather. The appearance of the balloon while aloft
is certainly curious. It appears to be rearing up on end, as if the
extremity saddled with the ballonet were weighted.
British and French captive balloon authorities are disposed to discount
the steadying effect of this attachment, and, indeed, to maintain that
it is a distinct disadvantage. It may hold the vessel steadier for the
purpose of observation, but at the same time it renders the balloon a
steadier target for hostile fire. On the other hand, the swaying of a
spherical balloon with the wind materially contributes to its safety.
A moving object, particularly when its oscillations are irregular
and incalculable, is an extremely difficult object at which to take
effective aim.
Seeing that even a small captive balloon is of appreciable
dimensions--from 25 to 33 feet or more in diameter--one might consider
it an easy object to hit. But experience has proved otherwise. In the
first place the colour of the balloon is distinctly protective. The
golden or yellowish tinge harmonises well with the daylight, even in
gloomy weather, while at night-time it blends excellently with the
moonlight. For effective observations a high altitude is undesirable. At
a height of 600 feet the horizon is about 28 miles from the observer,
as compared with the 3 miles constituting the range of vision from
the ground over perfectly flat country. Thus it will be seen that the
"spotter" up aloft has the command of a considerable tract.
Various ways and means of finding the range of a captive balloon have
been prepared, and tables innumerable are available for committal to
memory, while those weapons especially designed for aerial targets are
fitted with excellent range-finders and other instruments. The Germans,
with characteristic thoroughness, have devoted considerable attention
to this subject, but from the results which they have achieved up to
the present this guiding knowledge appears to be more spectacular and
impressive than effective.
To put a captive balloon out of action one must either riddle the
envelope, causing it to leak like a sieve, blow the vessel to pieces, or
ignite the highly inflammable gas with which it is inflated. Individual
rifle fire will inflict no tangible damage. A bullet, if it finds
its billet, will merely pass through the envelope and leave two small
punctures. True, these vents will allow the gas to escape, but this
action will proceed so slowly as to permit the vessel to remain aloft
long enough to enable the observer to complete his work. A lucky rifle
volley, or the stream of bullets from a machine gun may riddle the
envelope, precipitating a hurried descent, owing to the greater number
of perforations through which the gas is able to escape, but as a rule
the observer will be able to land safely.
Consequently the general practice is to shatter the aerostat, and to
this end either shrapnel, high explosive, or incendiary shells will be
used. The former must explode quite close to the balloon in order to
achieve the desired end, while the incendiary shell must actually
strike it, so as to fire the gas. The high explosive shell may explode
effectually some feet away from the vessel, inasmuch as in this instance
dependence is placed upon the terrific concussion produced by the
explosion which, acting upon the fragile fabric of the balloon, brings
about a complete collapse of the envelope. If a shrapnel is well placed
and explodes immediately above the balloon, the envelope will be torn to
shreds and a violent explosion of the gas will be precipitated. But as
a matter of fact, it is extremely difficult to place a shrapnel shell so
as to consummate this end. The range is not picked up easily, while
the timing of the fuse to bring about the explosion of the shell at the
critical moment is invariably a complex problem.
One favourite method of finding the range of a balloon is shown in the
accompanying diagrams. The artillery battery is at B and the captive
balloon, C, is anchored at A. On either side of B and at a specified
distance, observers O1 and O2 respectively are stationed. First a shell
is fired at "long" range, possibly the maximum range of the gun. It
bursts at D. As it has burst immediately in the line of sight of B, but
with the smoke obscured by the figure of the balloon C, it is obvious
to B that the explosion has occurred behind the objective, but at what
distance he cannot tell. To O1 and O2, however, it is seen to have burst
at a considerable distance behind C though to the former it appears to
have burst to the left and to the second observer to the right of the
target.
Another shell, at "short" range, is now fired, and it bursts at E. The
explosion takes place in the line of sight of B, who knows that he has
fired short of the balloon because the latter is eclipsed by the smoke.
But the two observers see that it is very short, and here again the
explosion appears to O1 to have occurred to the right of the target,
while to O2 it has evidently burst to the left of the aerostat, as
revealed by the relation of the position of the balloon to the bursting
of the shell shown in Fig. 3.
A third round is fired, and the shell explodes at F. In this instance
the explosion takes place below the balloon. Both the observers and the
artillery man concur in their deductions upon the point at which
the shell burst. But the shell must explode above the balloon, and
accordingly a fourth round is discharged and the shell bursts at G.
This appears to be above the balloon, inasmuch as the lines of sight
of the two observers and B converge at this point. But whether the
explosion occurs immediately above the vessel as is desired, it is
impossible to say definitely, because it may explode too far behind to
be effective. Consequently, if this shell should prove abortive, the
practice is to decrease the range gradually with each succeeding round
until the explosion occurs at the critical point, when, of course, the
balloon is destroyed. An interesting idea of the difficulty of picking
up the range of a captive balloon may be gathered from the fact that
some ten minutes are required to complete the operation.
But success is due more to luck than judgment. In the foregoing
explanation it is premised that the aerial vessel remains stationary,
which is an extremely unlikely contingency. While those upon the ground
are striving to pick up the range, the observer is equally active in his
efforts to baffle his opponents. The observer follows each successive,
round with keen interest, and when the shells appear to be bursting at
uncomfortably close quarters naturally he intimates to his colleagues
below that he desires his position to be changed, either by ascending to
a higher point or descending. In fact, he may be content to come to the
ground. Nor must the fact be overlooked that while the enemy is trying
to place the observer hors de combat, he is revealing the position of
his artillery, and the observer is equally industrious in picking up the
range of the hostile guns for the benefit of his friends below.
When the captive balloon is aloft in a wind the chances of the enemy
picking up the range thereof are extremely slender, as it is continually
swinging to and fro. While there is always the possibility of a shell
bursting at such a lucky moment as to demolish the aerial target, it is
generally conceded to be impossible to induce a shell to burst within
100 yards of a balloon, no matter how skilfully the hostile battery may
be operated.
The value of the captive balloon has been demonstrated very strikingly
throughout the attack upon the entrenched German positions in Flanders.
Owing to the undulating character of the dunes the "spotters" upon the
British monitors and battle ships are unable to obtain a sweeping view
of the country. Accordingly captive balloons are sent aloft in some
cases from the deck of the monitors, and in others from a suitable point
upon the beach itself. The aerial observer from his point of vantage is
able to pick up the positions of the German forces and artillery with
ease and to communicate the data thus gained to the British vessels,
although subjected to heavy and continuous hostile fire. The difficulty
of hitting a captive balloon has been graphically emphasised, inasmuch
as the German artillerists have failed to bring down a solitary balloon.
On the other hand the observer in the air is able to signal the results
of each salvo fired from the British battleships as they manoeuvre at
full speed up and down the coastline, while he keeps the fire of the
monitors concentrated upon the German positions until the latter have
been rendered untenable or demolished. The accuracy of the British
gun-fire has astonished even the Germans, but it has been directly
attributable to the rangefinder perched in the car of the captive
balloon and his rapid transmission of information to the vessels below.
The enthusiastic supporters of aerial navigation maintained that
the dirigible and the aeroplane would supersede the captive balloon
completely. But as a matter of fact the present conflict has established
the value of this factor more firmly than ever. There is not the
slightest possibility that the captive balloon sections of the
belligerents will be disbanded, especially those which have the
fruits of experience to guide them. The airship and the aeroplane have
accomplished wonders, but despite their achievements the captive balloon
has fully substantiated its value as a military unit in its particular
field of operations.