Page:EB1911 - Volume 20.djvu/255

HEAVY FIELD AND SIEGE] The floating pistons are tapered slightly inside towards the front to prevent violence in the running out action. The elevating gear, which can be placed on the left side of either the trail or the top carriage, actuates the arc K, bolted to the left side of the cradle. When the gun is fired on wheels (fig. 72) an anchorage buffer M, attached to the platform, checks the recoil, whilst the springs with which it is provided cause the carriage to return to its position.

EB1911 - Ordnance Fig 73.png . 73.—Diagram of British 6-in. B.L. Howitzer (70° elevation).

The United States 6&#8202;″ Howitzer.—This is a more modern equipment, its date being 1905. The howitzer is a short piece, 13 calibres long; it fires a 120-℔ shell with a muzzle velocity of 900 f.s. It has an extreme elevation of 45° and an effective range of 7000 yds. The weight behind the team is 705 cwt. The carriage is of peculiar construction (fig. 75). The howitzer is supported under its cradle, which is carried on trunnions seated in the top carriage. The cradle consists of three cylinders generally similar in arrangement and in functions to those described for the 4·7″ 60 pr. gun: the howitzer is made in a single forging and carries a lug on its breech end for the attachment of the recoil piston rod and the yoke for the rods of the spring cylinders; flanged rails are formed on its upper surface, which support it on its cradle. The top carriage rests on a framework called a “pintle bearing.” Flanges in the former engage under clips in the latter; the pintle bearing is riveted to the front part of the trail brackets, and forms a turn-table upon which the top carriage and all supported by it have a movement of 3° traverse on either side.

This movement of traverse is effected by a shaft and worm: the former is supported in a fixture attached to the left trail bracket, and the latter works in a nut pivoted to the top carriage.

EB1911 - Ordnance Fig 74.png . 74.—Hydraulic buffers of British 6-in. B.L. Howitzer. (N.B.—Spiral, instead of volute springs, are now used.)

Elevation is effected by a forging called the rocker. The rear part of the latter is U-shaped and passes under the gun, being attached to the cradle by a pivoted hook k. From either side of the U arms extend which embrace the cradle trunnions between the cradle and the cheeks of the top carriage so that the rocker can rotate about the cradle trunnions. The elevating gear is supported in lugs on the under side of the top carriage, while the upper end of the elevating screw is attached to the bottom of the rocker. The rocker thus moves in elevation in the top carriage and gives elevation to the cradle, and therefore to the gun, by means of the pivoted hook above referred to.

The brackets of the trail extend separately to the rear, sufficiently providing for free movements of recoil at any elevation; they are then joined by transoms and top and bottom plates and terminate in a detachable spade which is secured to the top of the trail in travelling. The axle is of special shape to admit of the movements of the cradle; it is lower in the middle than at the sides and is made in three parts, held together by shrinkage in cylinders formed in the sides of the pintle bearing.

A peculiarity of this carriage is that recoil is automatically shortened as elevation increases. Thus the length of recoil is 50″ at angles of firing from −5° to 0°, from 0° to 25° the 50″ is gradually reduced to 28″, which is not changed for higher angles. This is effected as follows: Four apertures are made in the piston of the recoil cylinder and there are two longitudinal throttling grooves in the walls of the cylinder. All apertures being open and deepest part of grooves in use would correspond to a 50″ recoil; apertures closed and grooves alone at work would mean a 28″ recoil. A rotating disk with apertures similar and similarly placed to those on the piston is carried by the piston rod and rests against the front of the piston, and is actuated during recoil by two lugs projecting into helical guide slots cut in the walls of the recoil cylinder. The latter is mounted so as to be capable of rotation in the cradle, and its outer surface carries teeth which engage with similar teeth in a ring surrounding the right spring cylinder. When the elevation is between 0° and 25° these latter teeth engage in special gearing which is seated in the hollow trunnion of the cradle and is attached to the right cheek of the top carriage. The buffer conditions are thus made to correspond with the elevation.

The mortar is a short piece of ordnance that is always fired from a bed. Changes in range are usually effected by varying the charge.

United States 3·6&#8202;″ Mortar.—This equipment is not modern; the piece was intended for vertical fire against troops in entrenchments; the mortar weighs 245 ℔, and its bed, which is made in a single casting of steel, 300 ℔. The latter rests in action on a wooden platform and is held down by ropes and pickets.

The German 8·4&#8202;″ Mortar.—This equipment is perhaps the heaviest field equipment existing. The mortar in action weighs about 4·9 tons; it has to be transported in a special vehicle and can only be fired from a platform; four hours are required for bringing it into action. Two platform wagons are attached to each mortar, weighing respectively 2·9 and 4·9 tons. The equipment can be moved at a walk on good roads, but two companies of infantry are always attached for haulage in case of need. A battery consists of 4 mortars, and 160 rounds are carried. The shell weighs 250 ℔ and carries a heavy charge of high explosive, with or without delay action fuze.

A special equipment designed by Messrs Krupp is shown in Plate vi., figs. 76 and 77. It is a mobile mounting for an 8·26″ mortar with constant long recoil, which is fired, like a howitzer, from its travelling carriage without a platform. This equipment weighs about 5 tons in action.

All the foregoing equipments may be considered mobile; that is to say, the batteries in which they are organized are self-contained, can move from place to place without external assistance, and may be employed on either field or siege duties. Their uses may be summed up as follows: The first object of the heavy artillery accompanying an army is to demolish the barrier forts or other frontier fortifications of a permanent nature in order to enable the army to penetrate into the enemy’s country. After this has been done, a small portion of this artillery will be employed in connexion with the siege of fortresses, while another, by far the more considerable portion, will accompany the advance of the field army.

Heavy Siege Units.—When a serious siege has to be undertaken it is necessary to organize one or more siege trains in addition to the troops of the field army. Both heavy and light siege units enter into the composition of a siege train. As to the armament of the latter, we have said that it is not exactly distinguishable from that of heavy field batteries, and it has already been described. That of the former is less definite. Heavy siege units are seldom mobile in the sense that light siege units are: the ordnance comprising the former has usually to be transported by some special means; thus it might be conveyed by ordinary rail or ship to some place from which special siege railways would admit of its conveyance to its place in battery, and probably great variety of calibre and mounting would exist. For example, during the siege of Sevastopol a civil engineer, Robert Mallet (1810–1881), designed a 36″ mortar; it did not, however, reach the seat of war; and in 1904 the Japanese made use of their 11·1″ coast howitzers at Port Arthur. At the siege manoeuvres in France in 1906 the heavy siege units were represented by their 6·1″ gun and their 10·7″ howitzer. The official British pieces are a 6″ gun and a 9·4″ howitzer. Generally speaking, whereas the most suitable armament of the light units can as a rule be foreseen, that of the heavy would depend very much on circumstances.