The automobile and the gun mounted thereon follow widely different lines. Some vehicles are designed especially for this duty, while others are improvisations, and be it noted, in passing, that many of the latter have proved more serviceable than the former. Still, the first-named is to be preferred, inasmuch as necessarily it is designed to meet the all-round requirements imposed, and consequently is better able to stand up to the intended work, whereas the extemporised vehicle is only serviceable under favourable conditions. The Krupp Company has evolved many designs of anti-aircraft motor-driven guns--"Archibalds" the British airmen term them with emphatic levity. They are sturdily-built vehicles fitted with heavy motors, developing from 40 to 50 horse-power, with the chassis not widely dissimilar from that adopted for motor-omnibus traffic. Consequently, they are not necessarily condemned to the high-roads, but within certain limits are able to travel across country, i.e., upon fields or other level expanses, where the soil is not unduly soft. But the very character of the problem rendered the evolution of the vehicle a somewhat perplexing matter. There were many factors which had to be taken into consideration, and it was possible to meet the imposed requirements only within certain limits. In the first place, the weight of the gun itself had to be kept down. It was obviously useless to overload the chassis. Again, the weight of the projectile and its velocity had to be borne in mind. A high velocity was imperative. Accordingly, an initial velocity varying from 2,200 to 2,700 feet per second, according to the calibre of the gun, was determined. Moreover, as mobility was an indispensable condition, the gun had to be so mounted that it could be fired from the motor-car even if the latter were travelling at high speed. This requirement entailed another difficulty. The gun had to be mounted in such a manner as to enable the gunner to train it easily and readily through the complete circle and through its complete range of vertical inclination. As the result of prolonged experiments it was ascertained that the most suitable arrangement was a pedestal mounting, either within a turret or upon an open deck. To meet the weight of the gun, as well as the strains and stresses incidental to firing, the chassis was strengthened, especially over the rear axle near which the mounting is placed.