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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 centimetresapproximately 2。75 inchesis 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 pedestalin 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 All