The object sought to be obtained is therefore to aim from in-board at an invisible target, the distance and direction of which are indicated by the Captain. It is consequently necessary that he shall be so placed as to obtain a distinct view of the enemy, or have suitable observers to inform him of his exact position.
320. In general, this sort of fire has been of little efficacy; but by the aid of a simple implement, readily made on board ship, it is believed that good results may be obtained, and particularly at night, when firing from guns on covered decks is now absolutely ineffective.
It consists of a simple metal or wooden batten, sliding in two beckets attached to the outer or inner sides of each of the brackets of the carriage, retained in any position by a thumb-screw. This batten is graduated by experiment or calculation for either the parallel or converging fire, for such points on the bow, beam, or quarter, as may be deemed advisable.
A small knob is screwed into the inner end of each batten, and a cod-line provided, with a loop in each end, somewhat longer than the width across the transom. If, then, one of the battens be drawn out to the graduation representing the degree of train required, the line stretched taut from the two knobs and hitched, and guns trained until this line is parallel to a mark on the deck, or one of the seams of the deck-plank—if they are parallel to the keel—the guns will all make the required angle, and may be fired simultaneously or in succession, as ordered.
321. The principal object in view, therefore, is so to prepare the training by anticipation, that when the smoke rises, or on sheering the vessel, the enemy shall be visible to all the Gun Captains at the same time; giving them the choice to fire at will, or on a given signal, if simultaneous fire be desired.
It diminishes the great disadvantages of guns on covered decks, where the Gun Captains can only with difficulty ascertain the direction of the enemy; and places the whole battery more completely under the control of the Commander.
322. The principal care of the Commander must be to keep his guns always bearing on the enemy, and never pass the limits of extreme train for all his guns, unless absolutely necessary in manoeuvring.
This he must regulate, either by one of the guns in his vicinity, or, better, by the aid of a bearing-plate, a species of plane-table which gives the angular bearing of the object.
323. Concentration of fire upon a particular part of an enemy's vessel may also be obtained by a general order for the guns to be aimed to strike that part when visible, leaving the Captains of guns to determine the proper time for firing, according to circumstances at the moment. This obviates the objections due to simultaneous firing, and would generally be equally effective at distances beyond point-blank. In this, as in all other cases of firing at sea, success depends mainly upon the skill, judgment, and coolness of the Captains of the guns.