When the elevating screw is used, a quoin should be at hand to place under the breech of the gun, when at extreme elevation, to relieve the screw from the shock of the discharge, and prevent a change of the elevation, as well as to take the place of the screw if it should be disabled. When the fire is continuous at the same distance, the lever of the elevating screw should be secured by a lanyard, to prevent the screw from turning and altering the elevation.
308. If a greater elevation for broadside-guns should be desired for any special purpose, it may be obtained by placing inclined planes behind the rear trucks, for them to recoil over and produce a corresponding depression of the muzzle of the gun as it comes within the port. But it will be observed that, beyond the elevation which the ports will admit of, the sights can no longer be taken by the tangent or any other top sight, as the upper sill of the port interferes. The gun must therefore be laid by the quoin and pendulum.
Additional depression may also be obtained by placing inclined planes for the front trucks to recoil upon, or by raising the breech by means of a wooden toggle placed vertically under it. One end of a tripping-line is fastened to the middle of the toggle, and the other to the breeching-bolt in the side of the ship; by this arrangement the toggle is tripped from its place at the commencement of the recoil, and the muzzle is raised so as to clear the port-sill by the preponderance of the breech.
NINTH COMMAND.
"READY—FIRE!"
"Waits patiently for the coincidence of the sights upon the object."
309. The exact moment for firing, at sea, necessarily varies with circumstances; but when these are favorable the following general principles should govern:
310. When the ship is steady, the gun should be fired when the line of sight is brought upon the object; but when the ship has much rolling motion, the moment for firing should be chosen a little before, so that the shot will probably leave the gun when the roll brings the line of sight upon the object aimed at.
When practicable, and too much time will not be lost, it will be best to fire when the vessel is on the top of a wave and just begins to roll towards the object. If the loss of time should be found objectionable, the gun may be fired at any other instant, when properly pointed, giving a preference, however, to the moment when rolling towards rather than when rolling from the object, and making due allowance for the probable change of elevation by the roll of the ship before the shot leaves the gun.
311. If, from any cause, the firing should be delayed after the gun has been pointed, it should be carefully pointed again before the order to fire is given.