There are two types of double-apron fence: the 4- and 2-pace fence and the 6- and 3-pace fence. The

Figure 8-20.-Double-apron fence.

4- and 2-pace fence (fig. 8-20) is the better obstacle of the two and is the type more commonly used. In this fence, the center pickets are 4 paces apart and the anchor pickets are 2 paces from the line of the center pickets and opposite the midpoint of the space between center pickets. The 6- and 3-pace fence follows the same pattern with pickets at 6- and 3-pace intervals. For this fence, less material and construction time are required, but the obstacle effect is substantially reduced, because with the longer wire spans, it is easier to raise the lower wires and crawl over or under them. Except for picket spacing, the 4- and 2-pace and the 6- and 3-pace fences are identical. Only the 4- and 2-pace fence is discussed in detail.

A 984-foot section of either type of double-apron fence is a platoon task normally requiring 1 1/2 hours, assuming 36 productive men per platoon. There are two operations in building a double-apron fence: (1) laying out and installing pickets and (2) installing wire. The first operation is nearly completed before starting the second. The second operation is started as men become

Figure 8-21.-Laying out anchor pickets,

available and the first operation has moved far enough ahead to avoid congestion. A platoon is normally assigned to build a 984-foot section.

Phase One

Divide the working party, if not organized in three squads, into three groups of approximately equal size. One squad lays out the long pickets along the center line of the fence at 4-pace intervals at the spots where they are to be installed and with their points toward the enemy. Another squad lays out the anchor pickets with points toward the enemy and positioned 2 paces each way from the center line and midway between the long pickets (fig. 8-21). The spacing is readily checked with along picket. The third squad installs all the pickets with the help of the two other squads, as the latter finishes the work of laying out the pickets. When installed, the lower notch or bottom eye of the long pickets should be approximately 4 inches off the ground to make passage difficult either over or under the bottom wires.

Phase Two

As the groups complete the first operation, they return to the head of the fence and begin installing wire. The order in which the wires are installed is shown in figure 8-20 and is further illustrated in figure 8-22. Take care to avoid having any of the men cutoff between the fence and the enemy. Divide the men into two- or four-man groups and have them proceed to install the wires in numerical order; that is, as soon as the men installing one wire have moved away from the beginning of the fence and are out of the way, the next wire should be started. Installation is as follows:

1. The No. 1 wire is the diagonal wire on the enemy side and is secured with a top-eye tie to all pickets. It is important to keep this wire tight.

Figure 8-22.-Sequence of installing wire in a double-apron fence.

2. The No. 2 wire is the trip wire on the enemy side of the fence and is secured to both diagonals just above the anchor picket with the apron tie. This wire must be tight enough and close enough to the ground to make passage over or under the wire difficult.

3. The No. 3 wire is an apron wire on the enemy side of the fence. It is secured to the first diagonal wire, and thereafter to each alternate diagonal, and then to the last diagonal wire. The No. 4 wire is also an apron wire on the enemy side of the fence. It is secured to the first diagonal wire (No. 1), thereafter to the diagonal wires which are not tied to the No. 3 wire, and then to the last diagonal wire. Apron wire Nos. 3 and 4 are equally spaced along the diagonal wire.

4. The No. 5 wire is the first one that is not started from the end anchor picket. It is started at the first, long picket and ended at the last, long picket. It is secured with the intermediate-eye tie and is stretched tightly to prevent passage over or under it.