In the early phases of the present war the German successes were in no
small part due to their offensive use of tanks and mechanized equipment. As
they have gone on the defensive the Germans have paid equal attention to the
development of antitank obstacles. The antitank ditch is one of the principal
antitank obstacles, to which the Germans have devoted considerable study.
German-designed antitank ditches normally have vertical faces on both
sides and not only on the side farthest from the approaching tank. Both faces
must be broken down, but the face which the tank must climb up presents the
greatest difficulty. The pick and shovel is likely to be the simplest and quickest
method of breaking down a vertical face. The shovels should be specially
prepared beforehand by bending the heads at right angles to the handle, so that the
men can work on a face from inside the trench and pull it down towards them.
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It will be necessary to use explosives where the soil is hard or the face is
high. Various methods have been tried including the placing of charges against
the vertical face or dug into the vertical face. Both of these methods have been
unsuccessful as the resulting ramp has proved to be far too steep for the tank to
climb. The only method that has been universally successful has been the placing
of charges as shown in Fig. 1, though it has the disadvantage of exposing the men
while placing the charge. In this method a minimum width of gap of 12 feet is
required. The charge is placed on the original ground level, or dug in flush with
the original ground level and tamped if time permits. Boxes containing 25 pounds
of TNT, or equivalent explosive, are placed in a line across the gap desired. If
the soil is not too compact, the charges can be placed 9 inches apart. If the soil
is hard and compact the boxes containing the charges should be touching so as to
increase the total charge. An alternative that has proved successful is the placing
of double charges at the ends where the tank tracks will cross (see Fig. 2).
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The distance from the back of the charge to the edge of the trench should
equal one-half of the depth of the face. If the trench is revetted with timber, the
revettment must be cut. This is done by dropping the necessary cutting charges
of TNT against the revettment in the form of an elongated pole charge. The
charge will vary according to the type of revettment. It should be placed
one-third of the way up the revettment from the bottom of the vertical face. (see
Fig. 1).
If the wall is revetted with concrete the sides as well as the bottom of the
panel to be blown out will have to be cut with explosives (see Fig. 3). All these
charges must be made up beforehand on planks. There should be no economy of
struts as close contact with the wall or revettment throughout the charge is
important. Unless the thickness of the concrete revettment is accurately known, a
larger charge than might appear necessary should be used in order to insure
destruction. The charges should be laid end to end in order to get complete cutting
action.
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All charges must be detonated simultaneously including those on top of the
trench, on both sides, and the revettment cutting charges. A detonating cap should
be used in every 25-pound cratering charge of TNT and at suitable intervals
along the revettment cutting charges. The entire demolition setup is
interconnected by means of primacord and leads are brought out to a central junction
where detonation can be safely initiated. In order to be on the safe side, all
primacord mains should be in duplicate. The junction box should be placed so
that the detonating waves go forward along the primacord with no undue bends.
The explosion which breaks down the sides of the ditch leaves loose pulverized
earth ramps on each face and loose earth in the bottom of the trench,
which must be leveled off with pick and shovel. The spoil forming the ramps is
likely to be very loose and soft, so that tanks will dig themselves in when
climbing the ramp and get stuck. It is the rear of the tank's tracks which tend to dig
in and belly the tank as it opens its throttle to climb out of the trench. To
prevent this, brushwood fascines must be made ready to provide a good surface on
the bottom of the ditch and resist the digging in by the rear end of the tank.
The fascines are laid crosswise and must be carefully made or they will
tend to provide a track that will be too steeply cambered and the tank will slip
off sideways. To prevent such sliding the fascines must be made wider at the
ends, than in the middle by placing the brushwood, of which the fascines are made,
with the thick ends outwards and the thinner parts towards the center (see Fig. 4). To
insure strength, the center of the fascines must be very securely and
tightly bound with wire. A reserve of fascines must be kept ready in the ditch
to strengthen the tank gap as it shows signs of breaking up. It is essential that
there be continuous maintenance of the gap while it is in use.