This part of the discussion deals with German wire technique, as observed in The Netherlands, Belgium, and France. On the beaches, barbed wire is usually erected in straight lines, parallel to the shore and in front of fortified areas. In the spaces between fortified areas the lines of wire jut out at right angles toward the sea.
The depth of wire obstacles around emplacements and fortified areas varies with the topography and importance of the site. In some places it may be 30 to 60 yards; in other positions the depth may range from 70 to 130 yards, or may go up to 200 yards. Generally, the distance from the outside edge of wire to the nearest pillbox or other firing position is not less than 30 yards.
Dense entanglements are installed in gullies and in the crevices of cliffs, whence the wire may continue as single fences along the top margin of the cliffs. The entanglements usually begin to thin out half-way up the side of gullies. In front of these obstacles the Germans sometimes erect small-mesh wire, apparently to slow up the employment of bangalore torpedoes.
The Germans often use wire to fence off all sides of a minefield. These fences consist of a single row of pickets with five or six strands of wire. In conjunction with road blocks, a wire entanglement or fence is employed on each side of the road, and the gap between is closed by movable gates of various types. Concrete walls and other more substantial types of barriers are now replacing wire entanglements as road blocks in many places. A thin belt of wire is usually erected outside of antitank ditches. Wire is employed on practically all wall barriers and concrete emplacements, which often have iron staples in them for the stringing of apron and other types of entanglements.
A new type of German barbed wire now in use is thicker than ordinary wire, is made of a noncorrosive metal, and is rectangular in section. It has three-quarter-inch barbs at intervals of 4 inches.
b. Specific Types
Some details of specific types of wire obstacles in The Netherlands, Belgium, and France are listed below. The dimensions are approximate.
(1) Knife rests.—Knife rests, or cheval-de-frise obstacles, strung with wire, have been observed on beaches above high-water mark. Some examples consist of four trestles connected by a cross bar. The dimensions are as follows:
|Height||_ _ _ _ _ _ _||4 feet|
|Span of trestle legs||_ _ _ _ _ _ _||4 feet|
|Distance between trestles||_ _ _ _ _ _ _||4 to 5 feet|
|Length of four-trestle unit||_ _ _ _ _ _ _||16 to 20 feet|
(2) Apron fences.—These may be single or double aprons. Screw pickets or angle-irons embedded in concrete to a depth of about 18 inches are used to hold them. Sometimes a coil of concertina may be placed under double-apron fences. Another variation is to place a coil of concertina on the tops of such fences. The dimensions are as follows:
|Height||_ _ _ _ _ _ _||4 to 5 feet|
|Height (with coil on top)||_ _ _ _ _ _ _||7 to 8 feet|
|Width||_ _ _ _ _ _ _||Up to 30 feet|
(3) Vertical fences.—Vertical fences are invariably installed in two or three lines, 4 to 8 feet apart. Each fence has five or six strands of wire, and is 4 to 6 feet high. Wooden posts, angle-irons, and screw pickets are used as supports. Various types of entanglements and mines are often used in the spaces between fences.
(4) Concertina fences.—Single, double, or triple coils of concertina are used with angle-irons or screw pickets. Triple coils are often affixed to the rails of the promenades that are so common along the beaches of western Europe.
(5) Trip fences.—Trip wires in diagonal or diamond-shaped trace are frequently found in front of major obstacles, usually between the high-water mark and the first barbed-wire entanglement, or they are erected in fields before main defensive positions or obstacles. Their dimensions are as follows:
|Height||_ _ _ _ _ _ _||4 to 6 inches|
|Length of each diagonal or diamond-shaped trace||_ _ _ _ _ _ _||4 to 6 feet|
|Width of whole obstacle||_ _ _ _ _ _ _||12 to 20 feet|
(6) Alarm wires.—There is evidence that many wires have some form of alarm device connected to them, such as grenades, small explosive charges, and insulated live wire, which would ring a bell if cut.
(7) Electrified wire.—Electrified barbed wire, held by insulators to pickets, has been reported, but it is not likely to be encountered on a large scale.
(8) Combined fences.—A typical combined fence may consist of the following units in the order given: a trip wire, a trestle fence or knife rest, and (10 to 20 yards farther back) an apron fence. The total depth of such a combination may be 30 to 60 yards. On the sea fronts of towns, the usual practice is to have an apron or knife-rest fence on the beach, and a concertina or apron fence on the top of the sea wall and promenade.
c. Standard Technique
For comparative purposes, some notes on available information about wire-obstacle practice, as prescribed in German training documents, are given below.
(1) Obstacle in depth.—This is constructed to a depth of approximately 33 feet, and consists of plain wire fences erected at intervals of about 5 feet and connected with more crisscrossed plain wire. (See fig. 7.) The spaces between the fences are filled in with barbed wire in spirals that are fastened to each other and to the pickets of the crisscross wire. Trees are used to support the wire if it is erected in woods. An obstacle in depth of this kind is usually erected in places where it is screened as far as possible from enemy observation, as, for instance, in woods, hollows, sunken roads, and heavily overgrown reverse slopes.
Figure 7.—Standard German barbed-wire obstacle in depth.
(2) Wire-netting fence.—The Germans prescribe the use of wire netting as a hasty obstacle against infantry. They state that it is most effective in woods and on the near side of hedges, and recommend that it be secured to the ground with wire and pickets. A training manual illustrates an example 6 feet 6 inches high.
(3) Trip-wire obstacles.—According to German practice, obstacles of
this type should be at least 30 feet in depth. They are formed by
driving into the ground irregular rows of wooden pickets, 2 feet long
and 3 inches in diameter, and stretching plain or barbed wire between
the pickets at a height of 4 to 8 inches. The interval between pickets is
10 to 13 feet, and between rows 7 to 10 feet. The freshly cut heads of
the pickets are painted to blend with the surroundings. These
obstacles can be effectively concealed in grass, heather, and gullies,
particularly if rusty wire is used, and they may be combined with