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furniture and equipment, must be formed in the interior of the available concrete masses; water must be laid on, lighting and heating provided for. Though hitherto it has not been thought desirable to provide power for working cupolas, etc., it has al- ready become necessary to include a power-room (dynamos and Diesel engines) in the equipment of the Feste.

Plan

FIG. 8. Flanking Organ (Metz).

Amongst these auxiliary arrangements, there is one, however, which during the World War proved to be of predominant im- portance ventilation. The fall of the forts of Liege and Antwerp was largely due to the ventilation arrangements proving inade- quate. Poisonous fumes from the burst shell penetrated the concrete fissured by its explosion, and filled the underground galleries of the fort, asphyxiating or disabling a large proportion of the already overstrained garrison. In the latter part of the war, the development of gas warfare added a further complica- tion, as it became unsafe to draw in air from outside. The solu- tion adopted by the French for the Verdun forts (which, it should be noted, no longer contained either main-armament or Iraditore artillery, but had become pure close-defence infantry works) was to deliver filtered air from a considerable distance, under slight pressure, to certain rooms in the fort, which were scaled against local air by air-tight doors or otherwise. All men working else- where than in these rooms wore gas-masks. Although the group principle of fortification, by dispersing the elements of defence, ipso facto dispenses with the subterranean labyrinths of the Belgian forts, and so reduces the effects of explosion fumes, the fact remains that the men in the armoured batteries and the traditore and flanking organs, must be protected from gas entering

either by embrasures, cupolas, seatings or fissures, while pure air must be supplied and foul air evacuated somehow. It may be, indeed, that the question of aeration, hitherto subsidiary, will become one directly affecting the fighting design.

Materials. Earth was always the common property of per- manent and of field fortification. Before 1914 concrete and ar- mour were reserved for permanent work, but during the World War both came into use for heavy field works as well. Further, as both in permanent and field work care is taken nowadays to disturb the natural earth as little as possible, and tunnelling freely employed, relief being kept down to a minimum, there remain only, as specially characteristic of permanent work, (a) the heavily armoured, deeply-sunk, mechanically highly finished gun-mounting, and (b) the great concrete mass. It is not un- reasonable to consider the necessity, or otherwise, of these ele- ments in a fortification scheme as a criterion of the necessity of " permanent fortification," using the words here in the technical sense for fortification of a kind that can only be carried out at leisure in peace conditions.

FIG. 9. Tradilore Battery the Bourges Casemate.

The justification of the elaborate gun-mounting under armour (the cupola, according to present practice) lies in its power to resist, for an indefinite time, counter-battery by the most power- ful guns available. That power was tested, during the World War, above all in the case of the Belgian fortresses and at Verdun. The gross results of these two trials were diametrically opposite the Belgian cupolas failed, usually through the failure of their surroundings but sometimes by their own defect, while the Verdun cupolas held out magnificently. Influenced by the general dis- trust of permanent work which the Belgian failures had pro- duced, the French had ceased to rely upon their forts for the flanking of the intervals, and the traditores had been actually disarmed before the attack of Feb. 21 1916. As this was the prin- cipal r61e allotted to the forts, the action of the few distant- defence guns in cupolas (safety-armament) could, ex hypothesi, be only a small part of the total artillery defence. But their powers of passive resistance were presumably tested as thoroughly as if they had been the protagonists of the main-armament, and practically none, save some minor cupolas for observation and machine-guns, were disabled at the close of the great siege. Yet they had endured an unexampled bombardment. Fort Vacherau- ville, for instance, was hit by no less than 2,250 shells, of 28-cm. and above two such shell for every three square metres of sur-