Page:EB1922 - Volume 31.djvu/1269

Rh The travelling platform proper was designed to render mobile a mounting which was already in use in fixed defences; it is limited to the use of good roads. The platform, a rectangular steel structure, is mounted for travelling on a pair of detachable axle-arms carrying rubber-tired wheels. Adjustable screws pass through nuts at the extremities of arms hinged to each corner, and these arms are swung

MOUNTING. 3-INCH, 20-CWT.. H.A.. MARK IV

TYPICAL ALSO FOR MARKSg ANDIV? LEFT SIDt ELEVATION.

( Working 11-0 inches i. Maximum 12-Q "

Body of mounting Cradle

Arc, elevating Seats Footrest

Wheel, hand, elevating gear Traversing gear Bracket, firing gear tever, rocking Rod, connecting Rod, firing Plates, clip Bearing, control rod Shaft, rack pinion Handle, firing gear Platform, sight corrector i This view does not show the traversing arc. M

FIG. 55. British anti-aircraft mounting for 3-10. gun

outwards to extend the base for firing; while, for travelling, the arms at one end are removed, the others being swung inwards and coupled to a motor-lorry. For firing, the platform is first raised by the screws and the wheels and axles removed; it is then lowered on to the ground and levelled. The underside is fitted with anchoring plates which, in conjunction with steel pickets, fix the platform for firing. The mounting is traversed on a circular base ring bolted to the platform.

FIG. 56. 3'6-in. anti-aircraft mounting, on caterpillar truck.

Fig 3 - 53 an d 54i showing the Schneider lO5-mm. (4'2-in.) equip- ment, model 1918, illustrate this form of anti-aircraft mounting. In fig. 53 the gun is in the firing and in fig. 54 in the travelling position. The ballistic and other particulars of this gun are as follows: calibre 105 mm.; length overall 425 cals. ; weight of shell 37 J Ib. ; M.V. 2,760 fs. ; range 15,400 yd.; weight of gun 36 cwt. ; travel- ling weight of gun and mounting (inclusive of limber perch) 9! tons ; weight of system in action 8 tons, including shield.

The caterpillar truck as a travelling and firing support owes its introduction to two reasons: first, the need for travelling an equip- ment over other than good roads; and secondly, to enable a heavier and more powerful mobile gun to be employed.

The truck used with the British 3-6-in. gun described below is approximately 15 tons in total weight and is tractor-drawn (fig. 56.)

The truck frame or platform, which consists of 4 transverse and 2 longitu- dinal girders, is adjustably mounted to permit of 9 longitudinal and 5 trans- verse levelling. A screw-operated steadying arm is hinged to each corner of the truck for use when firing; these arms are swung outwards and operated until they bear on the ground, the weight being then distributed over the arms and roller chains. A base ring is bolted to the top of the frame.

The caterpillar truck is least mobile of the 3 types, but does not restrict the equipment to road travelling. It has an advantage in that the gun is fired off the roller-chains and steadying arms unlike the platform proper, with which the wheels and axles must be removed for firing; while the levelling arrangements, though more complica- ted, are an improvement on the earlier adj usting screws.

As regards the mounting itself, the general principles of design may be illustrated by the British 3 in. (fig. 55). This may be either fixed or mobile, and the gun can be loaded and fired at any angle up to 90 of elevation, the height of the trunnions (nearly 5 ft.) giving clearance for the breech of the gun when firing at high elevations. The carriage is traversed on a live roller- ring which runs on the base ring, and is controlled by suitable gear. The ring cradle has a hydraulic buffer, spring recuperators, and is pivoted on trunnion roller-bearings at the top of the inter- mediate carriage ; the elevation is con- trolled through gearing in mesh with two arcs underneath the cradle. Seats, foot-rests and trays for the convenience

of the layers are adjustably attached to the intermediate carriage. The sights are of the rocking-bar type, and cross-connected to permit of dual control. When mounted in fixed defences, a training indicator, correctly oriented, is fixed to the emplacement floor.

The 4-in. mounting is generally similar to the 3-in., but, on account of weight, is used for fixed defences only. The gun can be fired up to 80 of elevation but must be depressed to 60 for loading. It has a tapered rod buffer and a hydro-pneumatic recuper- ator consisting in one liquid and two liquid-and-air cylinders.

The 3-6-in. mounting, designed on the rear-trunnioned principle, permits of all-round traverse and a maximum elevation of 90. It may be either fixed (when it is mounted on a pedestal), or mounted on a caterpillar truck as here shown in fig. 56. By adopting the rear- trunnion system, employing a ring-cradle, and rearwardly extending the intermediate carriage at the top, the gun is carried in a relatively low position which permits of loading from the ground, gives a maximum clearance for recoil, and increases the stability. Balancing springs are fitted under the front of the cradle to overcome the muzzle preponderance; and to balance the intermediate carriage, when on a caterpillar mount, an extension to carry a counterweight is formed at its front end.. The traversing gear is a 2-speed worm-and-rack drive. The elevating gears, of which one is operated on each side to embody the principle of the independent line of sight, are worm-and-arc-pinion drives. The recoil and recuperative arrangements consist in a rotary piston buffer with separate recoil and running-up valves, and a hydro-pneumatic recuperator of the floating piston type. The buffer is fitted with a spring-loaded tank and the recoils are controlled according to the elevation of the gun. (F. M. R.)

OREGON (see 20.242*). The pop. of Oregon in 1920 was 783,380 as against 672,756 in 1910, an increase of 1113,624 or 16-4% as compared with an increase of 62-7% during the preceding decade. The average number of inhabitants to the sq. m. in 1920 was 8-2 as against 7 in 1910. The sparsely settled areas, other than the national forests, are the plateau region of the south-eastern counties and the extreme south-western county. In all the south-eastern counties, excepting Malheur county lying along the Snake river, there was a decrease in pop. during the decade. The density of the rural pop. in the nine south-


 * These figures indicate the volume and page number of the previous article.