Outer Gunfire Area
[Aircraft Battle and
(Pursuit Area.
Inner Gunfire Area
Vulnerable Point
Aircraft Battle and
Pursuit Area.
Inner Gunfire Area
Vulnerable Point
FlG. 2 Night.
By taking the maps of any state and applying these principles to
the important towns, it will readily be seen that the matter is in
reality considerably more complicated than it at first appears. For
example, the defence area for Birmingham cannot be separated
from that for Coventry. The defence of London is closely associ-
ated with that of Woolwich, and both of these are intimately linked
with the defences of Gravesend and of Chatham ; so that it eventu-
ally becomes necessary to look upon the whole district south of a
line between the Wash and the Bristol Channel as a single area to
be provided with defences under one command. Therefore this
whole area will, for purposes of air defence, have an organization
independent of all those ordinary commands and military forma-
tions whose activities are limited by conventional lines on a map.
The same line of reasoning applies to forces in the field with their
" forward " areas, lines of communication, and bases; and necessi-
tates the problem of air defence being considered with reference to
the whole area of active operations, and not merely to that of all
the independent vulnerable points within it.
The principle illustrated in the diagram will be found applicable
to most cases, provided that consideration is given to the relative
urgency of demands for gun and aeroplane defence combined, and
of aeroplane defence alone. For the civil population, whilst applaud-
ing the courage and success of the airman, is ever apt to mingle with
its praise a demand for a gun. A gun is tangible and comforting ; it
can be seen and heard; and so it produces on the population a moral
effect which may be more than counterbalanced by the interference
it may cause to the defending airmen.
An instance, already alluded to, in which the principle requires
modification, is that of coastal towns and harbours, few of which
can be situated geographically so as to admit of the all-round dispo-
sition of defence illustrated. Here the sea intervenes to cut off
observer posts, searchlights, and guns, in addition to restricting the
area of manoeuvre for the defending aeroplanes by night. This
inroad into the defences offers the enemy an avenue of approach,
and necessitates considerable strengthening of the batteries within
range of and covering the sea in the neighbourhood. A certain
amount of defence may be afforded from vessels afloat, but reliance
cannot be placed on them for anything more than a temporary
assistance, as they may only be present for uncertain periods.
All that can be done is to increase the intensity of the gunfire
belt to seaward, and to provide aircraft detector posts and instru-
ments with a directional value in azimuth rather than vertically.
The latter serve as a partial substitute for the observer cordon by
giving somewhat distant warning of the approach of aircraft.
The defence of towns and ports separated from enemy territory
by sea alone thus requires maintenance in a state of instant readi-
ness for action, and so calls for a greater complement of personnel
than would be the case in defences situated inland.
The areas on either side of the dividing " line " between opposing
forces in the field, up to a distance of some miles from the dividing
line, were generally described during the World War as " forward "
areas. The areas behind the forward areas were usually termed
" back" areas; the latter term, however, was not generally taken to
refer to places outside the " theatre of war," though from the point
of view of aircraft action it was just as applicable.
In " forward " areas vulnerable points in the nature of men, guns,
animals, and ammunition stores are numerous, but as a rule well
distributed. In " back " areas they all tend to greater concentra-
tion. Protection is therefore more easily afforded in the former than
in the latter, and so the better targets for bombing machines will
be found as a rule in " back " areas.
The nearer the " line " the more intense will become the fire
of hostile ground artillery; this precludes the free use of searchlights
nearer than about 5,000 yd. from the " line," and necessitates the
distribution of anti-aircraft artillery in smaller fire units than is
possible at a greater range from the enemy.
Targets will be far more numerous in the forward area than in
rear of it, throwing much more work on the anti-aircraft artillery
situated near the line.
Applying the principle, as illustrated in the figures, to the prob-
lem in the field, a distortion of the diagram results, as in the cases
of coastal towns. The outer ring of guns (fig. l) is formed by the
guns " in the line " and such as can be spared to protect the flanks
and rear of the force. Within that ring, guns will be concentrated
closely around vulnerable points such ammunition dumps, hospi-
tals, etc., whilst the defending aeroplane will patrol in the space
which may be available between. The maintenance of communica-
tion between the forward guns in the shell area becomes a matter of
great difficulty and may require provision of special apparatus.
By night the guns " in the line " must rest as far as possible,
and employ themselves with observation duties. Searchlights in
the aeroplane battle and pursuit area nearest the " line " must
perforce be curtailed, and the aeroplane patrol lines withdrawn to
points which will admit of sufficient searchlights operating between
them and the attack.
VI. Some Possibilities of the Future.
Some limit to the speed of aircraft and the height at which
they can fly must be assumed, and, as far as the possibilities can
at present be imagined, heights up to 30,000 ft. and speeds of
200 m. per hour, together with powers of long endurance in the
air, may come within the range of practicability during the next
20 years or so. A successful development of the helicopter would
bring about a great change in the power of manoeuvre of aircraft,
and enormously increase the difficulties of the defence. Detection
of approaching aircraft will be rendered difficult by the silencing
of the machinery; their destruction by fire will be hampered by
the introduction of metal protection. Wireless aids to navigation
will decrease the difficulties of the pilot in thick weather, im-
provements in the landing power and stability of machines will
increase their immunity from storms; and all these conditions
will call for a greater state of readiness in the defence. On the
other hand, improvements in artillery will be necessary, and will
follow as a natural consequence. Inventions for the detection
of the locus of the source of sound will facilitate the accuracy
of searchlight work. These factors, in their turn, will impose
greater caution on the attack and give greater confidence to
pilots patrolling in defence. Aeroplanes now used in defence
will in the course of years become less localized in their work, and
will develop a tendency to operate more and more like battle-
fleets at sea. Such aerial fleets operating from their bases wilh
be likely to carry their own armaments and searchlights, and to
be accompanied by what we may call their " destroyer flights,"
which will assist them to seek out and find the enemy themselves.
The improvements which will produce this tendency will only
mature gradually, and danger will lie in the endeavour of the
ground or air services to assume entire responsibility for defence
against air raids before being in a position to do so. There must
be a long transition period during which cooperation between
air and ground units must be the strongest link in the chain of
Page:EB1922 - Volume 30.djvu/128
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94
AIR DEFENCE