5. Obstacles. These need only be constructed when two forces confront each other for a protracted period. The purpose of obstacles is to hold the enemy where he will be exposed to the most deadly fire; retard his advance; compel him to confine his movements to certain avenues of approach (this is especially valuable in night combats); and eliminate dead angles in front of the position. The presence of extensive obstacles forces the enemy to advance systematically. As a rule, they can only be removed by pioneers. They should not be located too near the position, as they are apt to be damaged by artillery fire directed at the position, and interfere with the defender's fire. When they are too far in front of the position, the defender will not be able to guard them and prevent their destruction. In general, they should not be more than 200 m. from the position. It is better to construct several lines of small obstacles than a single line of large ones. The requirement that obstacles must not interfere with the defender's fire, must not afford the enemy an opportunity to approach under cover, and must remain intact under hostile artillery fire, is best met by marshy ground and by wire entanglements. Obstacles should be provided with a slight glacis in order to prevent artillery fire from destroying them prematurely. When wire entanglements are too high, they are easily seen at a distance, and, although they are little damaged by artillery fire, the attacker can make preparations to remove them.
Russian Views.
A defensive position consists of an advanced position, a fighting line
with firing trenches and batteries, supporting points in rear, and, finally,
a fourth line, which serves as a rallying position. The key to a position,
which lay formerly in the line of supporting points, lies at present in the
firing trenches in which supporting points must be provided. (Colonel
Golenkin advocates the use of semi-circular works as supporting points,
and Lieutenant-Colonel Mordovin large closed works). "These semi-*circular
works are in a sense the anchors by means of which the firing
line clings to the position which it has occupied." It does not matter if
the enemy penetrates the first line and captures one or two of these
