LAND fe? WATER 
December 12, 1918 
a > s by the railway and the tunnelling of the hills, but the 
rinciple remains the same, to wit — that only a few defiles, 
whether they bo roads or railway tunnels, may be used by 
an army overcoming an obstacle in its advance. In the 
case of mountains and hill ranges, much the greater part 
of these defiles are arranged for one by nature. Roads 
nearly always follow the passes, and even the railway tunnels 
have to be chosen in spots where there is a special importance 
through the near approach of two valleys one to the other 
upon either side of the range. 
But in the case of a river the defiles to which an army 
is constrained is the result less of natural circumstance 
and more of the work of man. An army with its wheeled 
traffic must, as a rule, use bridges to overcome the obstacle 
of a river. It is true that it can make bridges of its own, 
whereas it cannot make mountain passes of its own, and in 
this respect it has a much greater choice of crossing. But a 
good established bridge gives far more rapid movement than 
a bridge temporarily thrown over on boats by the army 
itself, and as it gives greater rapidity of movement masters 
and, }f it is sufficiently close, can prevent the formation of 
the artificial bridge. An established bridge, especially in 
the case of a broad, deep, naxagable stream, nearly always 
means a town and — since the making of the bridge is a costly 
affair, especially in early times — each such bridge and town 
on a broad, navigable river nearly always means a concentra- 
tion of roads upon it. If you take any broad, navigable 
river — -the middle and lower Rhine, the lower Seine, the 
middle and lower Danube — any such obstacle, large or small, 
you will ajmost invariably find that the principal bridges 
come where there are towns on one bank or both, and that 
from these towns diverge in each case a fan of roads and often 
a fan of railways as well. In other words, the great advan- 
tage of such bridges is that you can concentrate upon them 
and diverge from them by many avenues, and the vital 
importance of their possession is that you command those 
avenues on both sides. The disadvantage, to an advancing 
army, of their destruction is not only a check but also loss of 
control over the avenues of advance beyond, until you have 
artificially thrown a new bridge across. - 
These factors in the value of permanent bridge-points over 
a broad stream are enormously increased to-day by the use 
of railways. There cannot be active railway traffic on a 
large scale over a bridge rapidly thrown haphazard by an 
army across a river. Across most types of such bridges you 
cannot put railway traffic at all. You cannot put heavy 
permanent traffic such as is necessary to supply a modern 
great army save over thoroughly established strong railway 
bridges spanning the stream. , 
Since any obstacle condemns an army crossing it to the 
use of defile?, and since while it is in those defiles an army 
is incapable of action (save with the tiny fraction of its head 
units), there follows the necessity of establishing what are 
called bridge-heads, and these bridge-heads, though they take 
their name from the obstacle of a river, are the same in 
character no matter what the obstacle may be, whether 
■ mountains, river, or marsh. 
WHAT BRIDGEHEADS ARE 
The essential definition of a bridge-head is this : a space 
occupied beyond the issue of a defile, such that it permits an 
army which has crossed the obstacle to deploy at such 
a distance from the enemy as shall make it secure from 
attack during the a'-t of deployment. Your army, while 
it is marching in column through the defile — -that is, across 
the bridge or through the pass in the mountains — cannot fight. 
Indeed, if it were caught in this column formation un- 
expectedly it would be destroyed. As its advanced units 
come out on the further side of the defile into open country 
they can spread out to the left and right, turning from a 
column into a line. As a matter of fact, of course, they do 
not turn into a mere line, but into a great agglomeration of 
men with a front line and reserves behind and the rest of it ; 
but in principle, the mancEuvre is a conversion from column 
into line. They could not effect this manoeuvre if they were 
being harassed by an enemy severely during the process. 
For instance, supposing we are in an epoch such as the 13th 
century, where a heavy cavalry charge could be launched from 
a distance of a mile or so and where portable missile weapons 
in the field had a range of 100 yards. An army under such 
circumstances debouching from an Alpine pass must be certain 
before it attempts to deploy upon the plain beyond that 
there is here no enemy force so close and of such a size that 
it could either by a charge of cavalry or by the use of missile 
weapons throw the first units into confusion as they came 
out from the mountains. For if that were to happen the whole 
column would be checked, pressure would continue upon 
the head of it before its advance could be completely stayed, 
and disaster would certainly follow. Therefore, every army 
condemned to pass through a defile must in some form or 
other establish a bridge-head. That is, it sends a force ahead 
of it, or secures by negotiation with powers upon the further 
side, or by the holding of a fortress upon the further side 
or in some other fashion, the certitude of being able to deploy 
during the delicate moment ivhen it is debouching from the 
defile. 
Such bridge-heads are an essential part in the organisation 
of any advance across any obstacle. Normally, in modern 
war, they have to be fought for. 
Take the example of the slight obstacle of the Lys last 
April. The enemy arrived at three bridges, two of which 
at least had been left undestroyed. His first care was to 
establish bridge-heads. Unless he had e;tablished bridge- 
, heads beyond the Lys he would have been held by the obstacle 
j^ntil an Allied reinforcement had come up. You had the same 
thing in the crossing of the broad canal south of Cambrai 
during the British advance in the summer. That perilous 
and heroic undertaking had for its object essentially the 
establishment of a bridge-head. Until the first troops had got 
this firm on the further side and got elbow room there, the 
main body could not follow. 
MAYENCE, COBLENZ, AND COLOGNE 
Under the conditions of an armistice — that is, under condi- 
tions where you are dictating to your enemy how he shall 
give you the military frui's of your victory without further 
fighting — you establish your own bridge-heads not by combat 
but by peaceful occupation, which the vanquished accept at 
the hands of the victors, and in this case the Allies have 
demanded the three bridge-heads Mayence, Coblenz, and 
Cologne, with a half-circle on the far bank upon a radius of 
30,000 yards — a distance corresponding to an effective zone 
of security under the conditions of a modern armistice. 
Let us see why these three points have been chosen. 
If you look at a map of the modern Xjierman Empire you 
discover that its central and western part is in the shape 
of an L. There is the main northern body comprising all 
the lower course of the great rivers — the Oder, the Elbe, 
the Weser, and the Rhine. This northern part is, in the main, 
flat. It has become industrially the core of the modern 
German effort. In religion it is for the most part Protestant ; 
its speech what is called Low German. Much the greater 
part of it consists in what geographers call the great Baltic 
Plain : Stretches of heaths, poor soil, and better soil in the 
river valleys, very flat, communications easy whether by road 
or by water, but production until modern times difficult 
from lack of fertility. Its northern Uttoral holds the great 
ports which were tlie basis of the Hanseatic League in the 
Middle Ages, and you have Bremen, Hamburg, Liibeck, 
Stettin, and the rest. The south-western part of this region 
contains that hill country separating the lower from the 
middle Rhine. So much for the main branch, the great body, 
geographically speaking, of that ephemeral modern experi- 
ment called the "German Empire," now happily dissolved 
and signifying in reality "that which was not only alhed to 
but ruled by Prussia." 
