6. Wire No. 9 is the diagonal apron wire on the friendly side of the fence and is secured with the top-eye tie to all pickets. Wire Nos. 10 and 11 are apron wires, and wire No. 12 is the trip wire on the friendly side of the fence. Wire No. 12 is installed in the same manner as wire No. 2.

7. If the fence is not satisfactorily tight when installed, wires are tightened by racking as described above.

STANDARD CONCERTINA FENCE

As an obstacle, inmost situations, the triple standard concertina fence is better than the double-apron fence. The material for it weighs about 50 percent more, but it is erected with about one half of the man-hours. Every concertina fence is secured firmly to the ground by driving staples at intenvals of not more than 6.6 feet. The staples are used on the single concertina fence and on the front concertina of the double and triple types. The two types of fence areas follows:

1. SINGLE CONCERTINA. This is one line of concertinas. It is erected quickly and easily but is not an effective obstacle in itself. It is used as an emergency entanglement or for the temporary closing of gaps between other obstacles. It is for such purposes that one roll of concertina maybe habitually carried on the front of each vehicle in combat units.

2. DOUBLE CONCERTINA. This consists of a double line of concertinas with no intend between lines. The two lines are installed with staggered joints.

As an obstacle, the double concertina is less effective than a well-emplaced, double-apron fence. It is used in some situations to supplement other obstacles in a band or zone.