Requests for retaliation should be made to this officer, and brigade H. Q. should be warned of the action taken.
Fire from howitzers and heavy batteries can, except in the case of the S. O. S. signal, only be obtained through brigade H. Q. If retaliatory fire is required from howitzers, it must be stated on what point it is wished that the fire should be directed.
Any trench mortaring by the enemy should be immediately reported to the officer commanding our trench mortars.
18. "S. O. S." AND "TEST" SIGNALS.—In the event of an infantry attack by the enemy, a mine being fired, or other emergency, the S. O. S. signal will be sent by the quickest route to the Field Artillery battery covering the trenches concerned.
The signal will be followed by the number of the trench, e.g., "S. O. S. B4."
The signal will be repeated to battalion H. Q., who will transmit it to brigade H. Q.
On receipt of the S. O. S. signal all batteries covering the trenches concerned will open a concentrated fire on the enemy's front line.
When necessity for fire no longer exists, a message to this effect will be sent to the artillery and to brigade H. Q.
In order to test the efficient working of the artillery lines, "test" messages will frequently be sent from the trenches to the supporting battery.
The number of the trench will always be sent, e.g., "Test A 6."