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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compressor back is withdrawn； either by the hand for manual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 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 e