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 beyond the range of the gun, or by carrying out baffling evolutions such as irregular undulating flight, wheeling, and climbing. According to the reports of the British and French airmen the "Archibald" has failed to establish the glowing reputation which was anticipated, for the simple reason that, unless it has a clear straight road and can maintain its high speed, it can easily be out-distanced by the fleet human bird.
The motor-car suffers from another serious disability. It cannot manoeuvre with sufficient celerity. For instance, if it is necessary to turn round in a narrow lane, valuable time is lost in the process, and this the airman turns to account. In hilly country it is at a still greater disadvantage, the inclines, gradients, and sinuosities of the roads restricting its effectiveness very pronouncedly. It must also be remembered that, relatively speaking, the "Archibald" offers a better target to the airman than the aeroplane offers to the man behind the anti-aircraft gun on the motor below. A few well-placed bombs are sufficient to induce the pursuers to cease their activities.
Even if the missiles fail to strike the motor-car itself they can wreak disaster in directly by rendering the road impassable or dangerous to negotiate at high speed. On the whole therefore, the "Archibald" is a greatly exaggerated weapon of offence against aircraft, and, so far as is known, has failed to fulfil expectations. In fact, the Germans have practically abandoned the idea of using it in the manner of a pursuing arm; they work the weapon as a fixture, depending upon the car merely as a means of moving it from point to point. Thus, in reality, it has been converted into a light field-piece, and may almost be included in the category of fixed weapons for combating aerial operations.
