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holds the compressor back is withdrawn, either by the hand for manual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
centimetres--approximately 2.75 inches--is 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 f