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of the perimeter as compared with group-works. The latter, therefore, allow of an extended perimeter for the same admissible intervals. Presently, as we have seen in the case of Metz, the perimeter attains an enormous length, and the ring opens out on the home side, becoming a gigantic redan or salient which comprises a whole region. The standard interval between work and work continues to be honoured at and near the exposed apex, but the gap increases towards the rear till near the root of the salient permanent work may give place to field work and simple utilization of natural obstacles, as in the " Nied position."

In the early igth century, the ring-fortress was practically an enlarged enceinte-fortress with the curtains omitted. Later, though perimeters increased (in order to prevent bombardment of the " nucleus "), the forts still contain the whole of the main armament and retain responsibility for the defence of the interval against methodical attack. The interval is organized according to the needs of minor tactics, so as to prevent the enemy pene- trating to the nucleus by any method but regular, large-scale attack. At the next stage (which is the most important in the evolution of ideas) the main artillery (except the safety-arma- ment) is taken out of the forts and deployed in the intervals, the forts becoming " strong points " on a line of battle which has to protect this artillery. It is this stage which is represented in fig. ii, taken indirectly from a semi-official Russian work of 1913, by Colonels Golyenkin and Yakovliev (which, incidentally, marks the acceptance in Russia, after long opposition, of the principle of armour protection).

FIG. II. Russian Fort, close-defence.

The " fort " is a large and elaborate close-defence work de- signed specially for the sweeping of the intervals by traditore batteries, immunity of these being secured by a full equipment of flanked ditches, quick-firing guns under armour and fighting shelters. The arc of fire of the Iraditores is sometimes carried unusually far forward, as it is laid down in principle that special flanking guns, in or out of the fort, must cover the ground from 1,200 yards in front to 700 yards behind the next fort. No part of the main-armament is included in the fort.

From fort to fort, the interval, it is laid down, should not ex- ceed about 4,500 yards. Otherwise, the responsibility placed on the Iraditores is too heavy (the average interval of Verdun, it may be remarked, is only about half this), and closed infantry work (Zw. in the plan) may sometimes be required to command some part of the interval that is not well covered by the forts. Frontally, the interval is held by a number of separate trench- positions formed with glacis foregrounds (V. Gl.) and provided with concrete fighting shelters (U.) and sometimes barracks (J.). Some of these positions have their own light quick-firing guns (Gst.) for flank protection. Four to five hundred yards in rear of this guarded obstacle are armoured batteries (H.P.B., K.P.B.), wired in, which contain the " safety " part of the main- armament with its ammunition. For the rest of the main-arma- ment, battery positions (D.W.) with (M.R.) shelters for detach- ments on duty (A.U.) and protected barracks for those in wait- ing (A.K.) are prepared 600-800 yd. behind the front line and connected up as required by trenches. For other batteries, told

off as a mobile reserve, positions are marked out (O.B.). The main magazines of the sector are shown at M.M. and barracks for the third relief of artillery at A.K. in rear.

Apart from the batteries of the safety-armament and occasional foreground-flanking guns not comprised in the forts, peace-time work on the intervals is limited in this example to the construc- tion of fighting shelters, barracks, magazines and the walls of battery positions. But, as soon as permanent work of any sort appears in the intervals, these begin to lose their blankness, and it is a short step to the modern conception of position-warfare the attack and defence of a long, shallow zone which contains in its forepart the close-defence and in its rear portion the distant- defence elements. In this zone, permanent work will, we may predict, be called upon to perform the services which field and heavy field work cannot perform. It will provide, generally, those of the essentials which cannot be improvised (such as the concreted or armoured infantry, machine-gun and flanking-gun positions, required in the more exposed sites), and in key sections, those which will make the local defence as nearly as possible inexpugnable. And since, as explained earlier, these key sections can be in many or most cases predetermined, whereas the exact position of the rest may vary according to the opponent's plan of campaign, the greater part, if not the whole, of the material protection obtainable with a given expense will tend to be con- centrated in them. Thus they may continue to be labelled with the names of towns or other localities as of old. But, essentially, they will be planned in relation to things outside and not to things inside, themselves. They will secure, or deny to the enemy, the use of certain ground or certain communications, definitely and completely. Locally, in order that the close-defence com- ponent may fully secure the operation of the distant-defence component, the permanently fortified key section may form a ring, or possess turned-back flanks of considerable length. But in the ensemble, and in many cases even locally, the tendency will be to reduce the depth and increase the frontage of permanent fortifications, so that the works of standard strength which can be built with the available funds may offer the widest direct and positive barrier to an enemy.

New Weapons in Siegecraft. The evolution, during the World War, of weapons essentially unlike those for which the perma- nent fortification above-outlined was designed to use and to meet, raises the question what modifications, if any, do these new weapons impose?

If the conclusion reached above be correct that permanent fortification has now become, from general causes, the backbone of position-warfare, instead of being a thing apart it follows that the new weapons will affect it in any case through their influence on position-warfare generally. Were it the case, for instance, that aerial warfare totally superseded land warfare, the ring-fortress might return in a new form as the means of pro- tection of flying bases. But such speculations would serve no useful purpose here, and it is preferable to confine ourselves to the modifications of detail to be expected in permanent fortifica- tion as such.

Chemical Warfare is a term covering several very different weapons. Smoke which " blankets " the defence organization, gas which disables the defenders, vapour-producers which infect areas, are all tactically dissimilar. The strength of chemical war- fare as against fixed defences lies in their fixity, its weakness in the fact that anti-gas protection is not limited, as it is in field warfare, to apparatus and devices that can stand rough usage and be car- ried without inconvenience by the already burdened soldier. One form of anti-gas defence has been mentioned above the supply of pure air under slight pressure to rooms sealed from contact with local air. Improvements on this line of progress would include more and more of the interior chambers of a work in the protected space, while other devices made the gun embrasures as gas-tight as possible. The most important defence against gas is the imperme- ability of the structure of the work itself, which practically means its solidity under bombardment. The direct influence of aircraft on permanent fortification is not easy to estimate. There is no limit to the power and flexibility of anti-aircraft guns sited in fixed defences. All fighting elements in the works are fully protected against the attack of super-heavy artillery, and a fortiori against that of air-bombs. The attack of traditore or caponniere embrasures by machine-gun fire from low-flying planes, if practicable, could be