Outline of the First Line. As was seen before, the original trace of the first line was established as a consequence of the needs of the battle. In the organization plan, it is necessary to introduce several modifications in this trace. The commander responsible for this change should place himself in the situation of the enemy and consider an attack upon his own lines. From this consideration he will introduce such modifications as will make this task as difficult as possible.
The responsibility of making this modification in the trace of the first line does not devolve upon the captain in the first line. As a rule if it were left to him few changes would be made because of lack of initiative on his part, or because of fear that if the line were captured he would be blamed for having changed it. This task falls upon the battalion commander who is responsible for the center of resistance, with the consent of the sector commander. The reason for this is that the sector commander is the only one of these officers who knows the subsequent use of this particular sector, whether for defensive or offensive purposes. If for defensive purposes the line may be carried as close to the enemy’s line as possible. If the sector is being organized for an offensive there must be enough distance between to keep his own line out of the zone of artillery dispersion when the target is the enemy’s line.
Cover Trench. In general all fire trenches have a second trench behind, called the doubling or cover trench. The use of the cover trench is not primarily for defensive purposes. It has special uses.
The majority of the troops in the first line are kept in the cover trench in shelters located there. The first line is habitually manned by only a sufficient number of men to assure observation and security. The rest of the garrison remains in the shelters of the cover trench to get as much rest as possible. It is very important that comfortable shelters be located in the doubling trench. If troops are exposed to the elements and bombardment their value decreases very rapidly. If the shelling becomes too severe the men in the first line retire to the shelters of the cover trench until the attack develops.
Another use of the cover trench in the defensive is to keep here a necessary number of troops for reinforcing the first line when necessary and for counterattack against the same if it is taken. This latter use establishes the distance between the two lines, which is from thirty to forty yards, so that hand grenades can be thrown from the cover trench into the first line.
Behind each support point there is usually a lateral communicating ditch called the circulating ditch which should not be confused with the cover trench.
Advance Posts. In front of the firing line certain advance posts are established. There are three kinds of these: listening, observation, and combat posts.
The listening post is not under the control of the commander of the support point but is in the service of the Intelligence Officer. It is furnished with a microphone for the purpose of picking up enemy’s telephone messages in the hostile line.
The observation post belongs to the sector and is used for purposes of observation and security.