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482 " the trenchy," and calls for more numerous communication- trenches, to which there is no further objection on the score either of concealment or economy of labour. In plan, the general result is an irregular skein of trenches, from 50 to 150 yards across, fol- lowing the contour of the front line, which itself undulates consid- erably and at certain points forms sharp cusps or salients of local importance. The closing-in of key positions for all-round defence, which figures in pre-war fortification, has become more thorough, and internal subdivision has converted these wired-in areas into the "Labyrinth" of Neuville-St. Vaast, the " Hohenzollern Redoubt " of Hulluch and the " Trapeze^ " of the Champagne battlefield. At the same time the interpretation of what constitutes a " key " posi- tion is different ; it is chosen in relation to the trench system rather than in relation to the ground. Mining plays no small part in the fight for the possession of particular hillocks, or trench lengths, with a view to improved observation or better defence. But from the standpoint of evolution, the most important difference between 1915 and 1914 work is the deliberate withdrawal of the infantry firing- line behind the military crest of the position. This was far from being universal in practice, but it had become the recognized ideal. As in permanent fortification, so also in field, the preservation of the close-defence element from bombardment was the motive of abandoning the command of the foreground. Stress begins to be laid, especially, on the local flanking of wire by machine-guns in covered emplacements. But again as in permanent fortifica- tion the needs of the artillery observer frequently conflict with those of the close-defence ; and each local problem, solved according to the value attached to these conflicting requirements at one time, has to be re-solved by fighting when the conditions change.

In this phase there are no marked innovations in the materials employed. The works are cut deeply in the earth and revetted by the conventional sandbags, hurdling, etc. of the text-books; details typical of trench-warfare fighting, such as trench blocks, sap-heads, island traverses, have been added. The " shelter " has become the " dugout," roofed in by layers of logs, house material, or in excep- tional cases railway iron, and as a rule, though not always, with- drawn from the front line into one of the parallels behind. Guns are casemated, and dugouts provided for their ammunition and per- sonnel as well as for a variety of command posts, aid posts, signal offices and the like.

la the second phase, which grew by degrees out of the first, the technique of fortification is modified owing to new conceptions of general tactics and to the bringing in of different materials. This is the phase that will remain forever typical of the western front campaigns. Its chief tactical characteristic is intense preparation and concentration of means of all sorts on the attack front, with a corresponding absence of the surprise element. The first conse- quences for fortification were: (a) the deepening of forward dug- outs, and their construction by mining methods which leave the natural earth undisturbed; (6) the quasi-certainty of losing the first trench system, at least temporarily, with the certainty of its being reduced to a tormented ruin in any case ; (c) reliance for close- defence upon the concealed machine-gun almost to the exclusion of other weapons; (d) multiplication of systems instead of multipli- cation of trenches in a system ; (e) more elaborate provision for the maintenance of supply for forward troops, represented in practice by the accumulation of stores in forward dumps of all sorts. It was in positions organized on these lines that the Germans fought out the battle of the Somme. But their Higher Command did not at first accept the implications of (6), and paid a heavy penalty for attempting the impossible task of holding the devastated front line in strength. Especially heavy was their loss in prisoners, due to the " deep " dugout, which was so deep that the men could not get out of it in time to man the trenches. Yet without adequate protection it was impossible to hold the front line, or any other line, under bombardment, even after converting it into a line of machine-gun posts; and the first modification due to the Somme experience was the introduction of the only alternative to the deep dugout, viz. concrete. This was a step of great importance, both tactically and technically. Concrete had already been used, here and there, to reinforce parts of an earth-system, and was constantjy employed in various back-area installations. But it was not till the latter part of 1916 that it became the principal material of " field " fortification. Instructions for mixing quick-setting con- crete, and even for making ferro-concrete, on the spot begin to figure in training manuals, and in the chief belligerent countries a new industry springs up for the manufacture of standard concrete elements, which are transported to the scene of operations and built up as required. The timber, mine-gallery framing hitherto used in dugouts gives place largely to standard semi-cylinders of corru- gated iron, also made at home and transported to the front in great numbers. Thus the ideal dugout for troops becomes a concrete structure lined with corrugated iron, proof against all field and me- dium calibres without being buried to any great depth; and the machine-gun emplacement and its dugout are fused in one concrete or ferro-concrete structure of the casemate type, famous in 1917 under the name of " pillbox " or " Mebu " (in full Maschinengewehr- Eisenbeton Unterstand). With this, the trench itself becomes of secondary importance. Though tradition and its undoubted use- fulness in all circumstances except those of great-battle days made

the command in all countries exceedingly unwilling to give up the trench altogether, it is the chain of dugouts and machine-gun case- mates, which, with the wire, defines the " position " of position- warfare at its highest development in the spring of 1917.

In the broadest sense, a " position " consists of several distinct, and more or less parallel, systems, each of which is at such a dis- tance from the one in front that the enemy's artillery must change position with all the attendant difficulties and delays of repairing communications through the battle-devastated area and mount a new attack. At intervals, a switch-line, designed on the same gen- eral principles as the parallel lines, is drawn so as to bolt off the area which may be lost in one battle phase. Between the first and second systems lies a zone in which a very active infantry resistance is carried on by means of " strong points," which are no longer labyrinths of the 1915 type but well protected and wired-in machine- gun strongholds, resembling in principle the traditore batteries of permanent fortification. With these as a basis, light trench-work will be run out in the directions required by the battle-situation from time to time, e.g. so as to fence off a lost sector; and for this purpose conveniently situated shell-holes are made defensible so as to constitute the framework of such lines. Tunnelling is largely used for short communications, especially where forward slopes have to be held so as to include artillery observation positions. The trench system bequeathed by the older methods is now broad (12 ft.) as well as deep, and is utilized as a covered- way, defensible in emergencies, rather than as a battle element. From 3-ft. to 5-ft. thickness of concrete (or ferro-concrete) over corrugated iron covers the casemated guns and machine-guns. With dugouts of similar design (the old deep dugouts are now sealed up or filled up by order of the command) these constitute the new defence system, whether disposed in lines or belts along the frontal systems or switch-lines, or scattered in the intermediate areas. Wire is now disposed in very wide belts, and does not conform to the direction of the trenches but lies in irregular salients and reentrants, each part under the eye of some machine-gun or trench-gun casemate. In short, the site of the " position " is governed by the needs of artillery observation, and by those of supply, while the organization of the site is based on the time, labour and material available for the construction of casemates and dugouts of concrete.

But " trench ' warfare has thereby divorced itself from the ele- ment which has been its characteristic for ages, the trench, and from June 1917 to the close of the World War is the period of zone- fortification. The elements of defence are now dispersed in innum- erable " nests," containing machine-guns, anti-tank guns, or counter- attack groups. The " position " attains hitherto unheard-of depth, and its forepart is held only by outposts, whose function is to police the ground in quiet times and give warning of assault in battle. Behind the " outpost zone " lies the " battle zone," in which ma- chine-gun and anti-tank-gun defence break up the attack, which a counter-stroke then sweeps back to its starting points. As a pre- caution, a " rear zone " is organized behind the battle-zone. But field-fortification has at this stage been completely merged in field tactics, which it assists, no longer by ingenious tracing of lines of defence, clearances of foreground, economical disposition of work- ing parties and materials, but simply by placing, at points indi- cated by the tactician, standard casemates and personal shelters, bor- rowed from the practice and made with the materials of permanent fortification.

Thus, while permanent fortification is concentrating its stock of ideas and devices upon the task of holding a long front of diminished depth, without any yielding of ground whatever, against the heaviest bombardments, field tactics have become fluid and mobile, ground being lost and won almost as readily as in the days of " manoeuvre " warfare, though by different methods. It is at the points of junction between permanent fronts and field fronts, w here particular features of ground are neither quite indispensable nor yet of negligible im- portance, that a field-fortification of the future will presumably find its proper scope. Like the zone-fortification of 19178, but to a further extent, it will have at its disposal many of the forms and methods of permanent fortification. (The illustrations to this article are reproduced by permission of MM. The Librairie Berger-Levrault, of Paris, from La Revue du Genie Militaire.) (C. F. A.)

SIENKIEWICZ, HENRYK (1846-1916), Polish novelist (see 25.54), died at Vevey, Switzerland, Nov. 14 1916.

SIERRA LEONE (see 25.54). There was a modification of the S.E. frontier in 1911, when Sierre Leone acquired the Kanre-Lahun district from Liberia in exchange for a district on the Morro river. The new boundary was delimited in 1913-4, Col. Cowie being the chief British commissioner. The total area of the colony and protectorate is estimated at 31,000 sq. miles. The census of 1911, partly based on estimates, gave a population of 1,402,878, Freetown, capital and chief port, having 34,090 inhabitants. The European population numbered about 1,000, that of the colony (as distinct from the protectorate) being 702, including 62 women; the Sierra Leonians some 70,000. There were also some hundred Syrians, almost all traders.