Land & Water 
April 1 8, 1 91 8 
even if your front has not a concave shape, for it exists 
when your most vital and necessary communications (which 
to-day, in spite of the extension of petrol traffic, still take 
the rare and expensive shape of railways) give you more 
rapid movement. For instance, your front might be actually 
convex as in H-K, but if your lateral communications were 
short and convenient hke M-N, while those of your opponent 
were long and inconvenient like 0-P, you would still have 
the advantage of what could technically be called interior 
lines, for you could move a unit from M to N more rapidly 
than your opponent couM move one from P to O. 
With this consideration in mind we have only to look at 
the railway map of Northern France and Belgium to see 
that the enemy here, although the front as a whole is not 
concave, has this advantage, and if we consider not only 
the northern part from the Arras-Amiens sector to the sea, 
but the whole line from AlSace to the sea, the greater distance 
through which the Allies must move to meet an enemy 
concentration is still more apparent. 
(5) Apart from this advantage in possessing what were 
virtually interior lines, which the enemy would enjoy if he 
chose this sector for his second offensive, there were certain 
local advantages which will appear more clearly when we 
discuss the action in detail. He had the great town of Lille 
in which to mass unobserved ; it was screened by the Aubers 
Ridge ; and above all, certain vital nodal points of commu- 
nication lay dangerously close to our front, notably Hazebrouck, 
Cassel and B^thune. If the reader will look at map III. 
which indicates the railways and main roads of the northern 
British front he will see the capital importance of these three 
points : Hazebrouck, Bethune and Cassel. 
Everything coming up from the south directly by rail 
must go through Bethune. Everything com! ng indirectly f rom' 
the south by the Boulogne railway, or directly from the 
north and west, the Ports of the Channel, must go through 
Hazebrouck junction. The only line excepted is the 
insufficient single coastal line Calais-Dunkirk. Save 
round by the coastal road, all road vehicles supplying and 
evacuating that front converge directly upon and must pass 
through Cassel. The sea was not far behind and there 
could be no rapid retirement of a large force beyond a sea 
line. 
(6) For what it is worth, there was the moral effect of 
an attack developing close to and threatening that highlv 
sensitive point the Straits of the Channel, the shortest and 
most direct communication between this country and its 
forces overseas.' But this must be set against a corresponding 
disadvantage which will be mentioned in a moment. 
So much being safd, we may equally tabulate the 
disadvantages and therefore risks which the choice of this 
sector would entail and which were as well known to the 
enemy as to ourselves. 
(r) It was the sector upon which reinforcements from this 
country could be poured most rapidly and the one behind 
which was the largest and most immediate supply of material 
as well as of men. 
(2) Upon one flank at least, that to the north, was the 
strong position of the Messines Ridge, continued by the strong 
position of the Passchendaele Ridge. To the south there 
was no equally strong flank, and it is on this account, as we 
shall see, that the enemy in his first plan made Bethune 
his chief objective — an objective wliich he failed to reach 
through the gallantry of the Lancashire troops. He knew 
then that if he did not succeed upon his left at Bethune 
his right would almost certainly be held on the Wytschaete- 
Messines heights and th%t he would be condemned to action 
upon the comparatively narrow front of 10 miles. 
(3) The triple lines in front of him — that is, the defensive 
zone which he had to break — ran through difficult, marshy 
ground, cut by numerous dykes, and the countryside having 
been densely populated before the war was fuU of strong 
posts in the ruins of cottages and farms. The enemy was 
therefore well justified in boasting of a special feat when he 
proved his capacity to break through this long-prepared and 
difficult organisation. Further, there lay immediately 
behind this defensive zone an obstacle, not very formidable, 
indeed, but still not negligible, in the shape of the Lys River. 
This little stream is a partly canalised piece of water, quite 
narrow (hardly anywhere 100 feet across), and in most places 
fordable so far as depth is concerned ; but it has a muddj' 
bottom, and the approaches are often marshy. 
(4) Any such offensive would, after the failure of his main 
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