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(VIII.) ANTI-AIRCRAFT EQUIPMENTS

On the advent of aircraft in practical offensive operations, it was found that the existing types of artillery equipment, both mobile and fixed, were hopelessly deficient in the essential qual- ities necessary for effective results. The speed and height at which aircraft operate are factors of great importance, as they combine to cause a considerable angular displacement during the time of flight of a projectile. The essential characteristics

FIG. 52. British 3-ton lorry, with 12-pdr. gun.

FIG. 5

required in a gun are high velocity, high rate of fire and capa- bility of being loaded at any angle of elevation, including means to prevent the round slipping back after loading. And the carriage must be designed to permit of the gun being loaded, laid and fired at all angles of elevation and traverse. The design must ensure a level platform so that, for accuracy of fire, the gun may pivot truly in the vertical and horizontal planes.

FIG. 53. Schneider iO5-mm. gun, on anti-aircraft mounting. Firing position.

Few specially designed A.A. equipments existed in any country and of these the greater part were constructed for fixed emplace- ments. In some countries these were augmented by makeshift mountings which usually consisted in a framework of pivot and plat- form in which the service field gun and carriage could be placed bodily. Soon, however, it became apparent that mobile as well as fixed guns were required.

To meet this need the British adapted a certain number of 13-pdr. and l8-pdr. guns, which were mounted on motor lorries. These answered the purpose for a time, but in view of the necessity for a gun having a higher M.V. than these, the ij-pdr. of o cwt. was evolved. This gun was practically a combination of the two:

externally, its dimensions were those of the l8-pdr. , and internally it had the bore of a 13-pdr. and chamber of an l8-pdr. ; that is to say, it fired the 13-pdr. shell with the l8-pdr. charge. The breech mechanism was practically the same as that of the l8-pdr. field gun with the addition of a cartridge-retaining catch, but the striker was modified so as to be cocked automatically on opening the breech.

With fixed mountings the requirements of the carriage can be met by designing the intermediate carriage to permit of the high elevation, and mounting it on live rollers on a base ring to give all- round traverse. The base ring is secured by bolts to anchoring plates embedded in a concrete emplacement, additional nuts for levelling being provided.

The design of a mobile carriage is limited principally as regards weight. The pre-war attempts to design a mobile anti-aircraft carriage were largely adaptations of the field carriage, for example the Deport 7S-mm. combined field and anti-aircraft equipment.

But the limited traverse and elevation which are inherent draw- backs in a field carriage prevent the mobile anti-aircraft equipment from being built up on the basic structure of a trail, axletree and wheels, and travelled with a limber like a field carriage. The design must be essentially the same as that of the fixed mounting, but the base ring must be mounted on a wheeled structure; further, road mobility as an entity is desirable, and, horse-draught not being up to the weight, mechanical traction must be resorted to.

The form of track as defined by rail, road and cross-country naturally assumes great importance. For railway travelling self- propelled unit-vehicles could be readily constructed; but restriction to a permanent way renders their use impracticable on a fluid front, while, for permanent defences, fixed mountings would be used.

FIG. 54. Schneider iO5-mm. gun, on anti-aircraft mounting. Travelling position.

For road mobility there are two alternatives: a self-propelled vehicle such as the motor-lorry or a tractor-drawn vehicle. In accordance with the law governing the maximum axle-load, the weight restricts the use of the lorry to comparatively light equip- ments. Thus, for the mounting of medium guns a special type of travelling platform, lorry-drawn, is generally employed.

For cross-country travelling ordinary wheels are useless, the pre- vailing method being to employ caterpillars or wheels running on chain tracks. In this connexion the automobile type of vehicle may be utilized for light guns; but for medium guns the base ring of the mounting would probably be supported on a framework pivoted on the axles of a tractor-drawn, caterpillar mount.

The types of wheeled structure which have been evolved may be given as follows: the motor-lorry, the travelling platform with detachable axles and rubber-tired wheels, the caterpillar truck.

The 3-ton lorry (fig. 52), the first type of wheeled structure to be used, was employed as a travelling and firing platform for the 12-pdr. coast-defence gun and the 13-pdr. horse-artillery gun, both of which were adapted to a suitable pedestal mount fixed to the lorry.

With intent to maintain approximately a constant load on the steering wheels whether the vehicle be empty or loaded, the lorry is designed on the cantilever principle. This ensures easy steering, but entails the whole of the useful load being borne by the rear axle. To preserve this principle, the pedestal was fixed to a steel base plate bolted to the chassis frame directly over the rear axle. When travelling the springs of the lorry act to reduce travelling stresses; but as a stable and level platform is necessary for firing, the gun cannot be fired off the lorry wheels. For this purpose, the lorry is supported on 4 adjustable screws mounted at the ends of steel beams fitted to the underside of the chassis; the screws rest on packing pieces, and are manipulated until the weight is taken off the wheels and the platform levelled.

For light equipments and travelling on good roads, the lorry is a convenient platform, as it provides the tractive power and carries the gun, ammunition, stores and personnel within one vehicle. The latest equipment to be mounted on a 5-ton lorry is the 3-in. mount- ing modified to take the IJ-pdr., g-cwt. gun.