4. Fire will be immediately concentrated on any machine gun that comes into action. With the German gun prolonged firing heats the water in the jacket to the boiling point and puffs of steam are given off. Do not be deceived into thinking that this necessarily gives away the position of the gun, for this steam has been piped to a distant place and allowed to escape so as to draw fire that otherwise might be directed on the real position of the gun. 5. On signallers or runners. These are carrying information that will probably be of benefit to the enemy's commander. You will appreciate the necessity of preventing this. 6. On an enemy showing a flank. No opportunity must be lost to fire upon an enemy that exposes his flank. The fire of a single rifleman down the flank may cause a whole line to retreat. USE OF RIFLE GRENADES Rifle grenades are capable of causing more losses to the enemy than bombardment. The rifle grenade arrives at its destination unexpectedly without any noise; it explodes before one has even time to get out of the way. As it does not arrive at fixed hours like the bombardment, the enemy cannot continually avoid it by taking refuge in his dugouts and shelters; when he is moving about a trench which is subject to rifle grenading he must be continually on the alert. This perpetual menace, hour in and hour out, day in and day out, renders his sojourn in the trenches extremely disagreeable. Before rifle grenades are thrown careful observation of the opposing trench must have been made to determine the point where the grenade is likely to do the greatest damage. Rifles are placed in the aiming racks and the grenades fired from time to time, day and night, at moments when it seems propitious. In this way a sentinel may be taken by surprise; a non-commissioned officer or officer may be caught unawares. It should be remembered that we will probably be able to throw twenty grenades to the enemy's one. Advantage should always be taken of this munitions superiority. Every man of the enemy we can put out of action is one less to kill us in the advance which will eventually come. Sometimes the enemy will try to reply. Here is where our munitions superiority comes in again. We can fairly shower him with grenades and make him take to his shelters. It may be advisable to execute a sudden burst of grenade fire. This is started by a volley and followed by fire at will. When the artillery has destroyed parts of the enemy's trenches or makes breaches in his obstacles by day he will endeavor to repair them at night. He may be considerably annoyed and losses inflicted upon him by a well-directed shower of rifle grenades arriving at points where his working parties are located. To make this effective the rifle racks should be placed in position and secured during the day after trial shots have demonstrated conclusively the direction and angle for them. SHELLING