Operation.—In firing shells the mortar should be surrounded by earth or sand, preferably placed in sacks. The fuse for all shells is very rapid and should be ignited by attaching the port fire to a long stick.
All of the old type Signal Corps mortars, originally designed to withstand a pressure of 1,000 pounds per square inch, and made of ordinary iron pipe, are considered unsafe and should be immediately destroyed. The new mortars, recently made for the Signal Corps by the Ordnance Department, are of cold-drawn steel having a tensile strength of 6,000 pounds per square inch, which is more than the maximum pressure for firing any of the Signal Corps bombs. They are stamped "Signal Corps, U. S. A., Model 1907," or "Rocket Gun, Watertown Arsenal, 1907."
The sequence rocket is prepared for use by attaching red or white sections to the base in such a combination as to form letters of the alphabet which it is desired to use. Letters containing the same color in sequence are very difficult to read and should be avoided whenever possible. If necessary to use them, blank sections furnished for the purpose should be inserted between the units. The base of the rocket will secure six units.
When rockets are to be fired the sticks must be firmly attached, the rocket placed upright in a trough, upon a frame, or against a post. If the fuse is beneath the paper covering the "choke" orifice, the paper should be torn off and the rocket ignited by a port fire. In the rockets now used the fuse extends through the covering and can be lighted direct. If the night be damp this fuse should be exposed only a moment before the rocket is fired. If several rockets are to be fired in succession it is well to prepare them all at the same time, and to have them all stood upright, but each separated from the other at a distance of at least 6 feet, else one may ignite the other accidentally. In firing for chronosemic signals, one rocket ought to be kept ready upon the frame and in reserve, to be fired in place of one that fails.
If a rocket misses fire it is to be taken from the stand and laid on the ground. Its place is at once supplied by a similar rocket, fired in its stead. The failing rocket is laid on the ground pointed away from the station in order that if it has only hung fire and should afterwards ignite it may not disarrange the signal shown or injure any one of the party. If the wind blows freshly the rocket to be fired should be inclined slightly against the wind.
Signal rockets and shells are furnished in sealed cans and should not be removed therefrom until ready for use. Strict economy should be observed in the use of these articles and on no account should they be used for purposes of display.
Employment.—Rockets and shells are especially valuable in making preconcerted or emergency signals. On account of the great amount of ammunition required it is impracticable to spell out messages with them. These articles should be supplied to outposts, detached stations, etc., to be used for signaling the approach of the enemy or the happening of unexpected events, the necessity for promptly knowing which is important.
THE SEMAPHORE.
If signal stations are to be permanently occupied, and it is impracticable to electrically connect them, communication may be facilitated by erecting semaphores.
Semaphores, while primarily used for day signaling, can be advantageously used at night by attaching lights to the arms.