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 enhances the possibility of breakdown at a critical moment.
For such arms a special and substantial chassis is imperative, while the
motive power and gearing must be adapted to the circumstances.

Motor-mounted anti-aircraft weapons, however, have not proved an
unqualified success. The fact that the vehicles are condemned to the
high roads, or at least to comparatively smooth and level ground,
constitutes a severe handicap. Again, when travelling at high speed, and
this is essential when pursuing a fast aeroplane, the accurate laying
of the weapon is extremely difficult, owing to the oscillation of the
vehicle itself, especially if the road surface is in a bad condition.
The sighting arrangements are of a wonderfully complete character, as
described elsewhere, but the irregular rolling movement arising from
high speed is a nullifying quantity. It is tolerably easy for the
aircraft, especially an aeroplane, to evade successful pursuit, either
by rising to an elevation bey