Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/325

GUNNERY 309 a small proportion of shrapnel shell. In order to strike vessels steaming past at high speed, great accuracy, com bined with rapidity of fire, is requisite. The guns are aimed either by eye or map, according to the nature of the coast. In the former case, the detachment commander estimates the range, gives the necessary elevation by means FIG. 29. 100-ton Gun (section). of the tangent sight, directs the line of fire according to his judgment, jumps down and gives the word to fire allowing for the vessel s motion and the time of the projectile s flight. The map system has been recently perfected by Cap tain Watkin, R.A. tkin s In it the whole navi- > gable front com- em - manded by the bat- FlG - 30. 100-ton Gun (section of groove). tery is plotted down in small squares numbered and lettered. Tables of the distances of the centres of these squares, the degree of training on the traversing arc required to lay the gun on the desired square, together with the actual elevation necessary to deposit the shot in that square, are constructed for each group of guns. FIG. 31. Watkin Position-finder. In fig. 31 F is a fort defending the channel; ABFC the line of shore; O the object to be hit, a vessel passing. A, B, and C are stations of observation. In a convenient spot the commanding officer of the artillery in the fort places the map, over which play two arms A O , C O kept constantly parallel to the tvo lines of sight AO, CO, by means of mechanism actuated by currents of electricity transmitted by a cable connecting A and A , C and . As A C repre sents, on the scale of the map, the distance AC, the junction O represents on the same scale the position and distance of the object O. Tell-tales are distributed in the casemates, which constantly exhibit the number of the square over which the vessel is passing, showing the position of the ship, so that when the gun, or group of guns, are loaded, they can be either laid in the ordinary way, taking the range from the tables, or, if the object is invisible from the casemate, by trailing the gun round till the number of degrees indicated by the tell-tale agrees with the reading on the traversing arc, and giving elevation to suit the range. The arcs showing the direction of the guns are so arranged that guns trailed to any given number of degrees are parallel with each other. Supposing that from smoke or other cause the object cannot be distinguished from C, an observer is placed at B, and the arm is shifted from C to B . The practical working of the system is as follows. The commanding officer watches the course of a vessel as indicated to him by the arms on the map, the observers at A and C con stantly following the centre of the object with their glasses. He telegraphs to the battery orders to load and lay, in accordance with the instructions given for each square of the map, and transmitted to the tell-tales. As the vessel passes over the square for which the guns are laid, the commanding officer can fire electrically the group of guns by pressing a key with his finger, or he may direct each detachment to keep up independent practice, laying in accordance with the indications sent by him through the tell-tale. The arrangements for exploding submarine mines or fixed torpedoes, where hostile vessels are passing close to them, are somewhat of the same character as those above described. 2. The land-front guns of fortresses shown in the table Guns o are intended to overpower and quell the fire of any pieces <*e f enc( which can be brought against them by a besieger. They are very largely supplemented in most fortified places by a number of the old smooth-bored guns and carronades, which are well adapted for the use of case shot at close quarters, for sweeping the glacis, and for the defence of ditches. The rifled guns throw common shell into the siege works, and where possible among the enemy s material. They harass his working parties and reliefs with shrapnel, and endeavour to cut down his parapets and dismount his artillery by direct fire. 3. Siege-train guns accompany an army on a campaign Guns o] where great mobility is not required, and where it is neces- attack, sary to reduce fortified places. They should be the most powerful pieces which the means of transport will permit. In the more civilized parts of the world, where roads and climate are favourable, it is generally considered that about 70 cwt. is the heaviest weight of piece that can be carried with an army. In less favourable countries it is frequently impossible to transport more than half that weight. The early rifled siege-train guns were grouped into two classes. A unit of the heavy train comprised 64 prs. of 64 cwt 8 40 ,, of35 ,, 8 8" howitzers of 46 cwt 14(figs. 32, 33). A unit of the light train comprised 40 prs. of 35 cwt 10 25 ,, of 18 ,, 10 6 3" howitzers of 18 cwt 10 Lately 8 - 0" howitzers of 70 cwt. and G G" howitzers of 35 cwt. have been introduced, but their allotment has not

yet been settled. Siege guns are supplied with special shell,