The fortresses guarding Warsaw and the Russian frontier were quickly taken in the Teutonic advance of 1915, either by manoeu vring the defenders out of their fortifications, or, as at Novo Georgievsk, by shattering them with the heavy siege guns. The fortress of Ossowetz on the Niemen-Bobr-Narew line had a different history. Ossowetz stands on , the up their heavy siege guns. The Russian batter ies were, however, so well concealed that they suffered very little damage and succeeded in silencing several German batteries. As the warm weather advanced, the marshes made it difficult for the Germans to emplace their guns.' Ossowetz, although first attacked in February 1915, did not fall until 22 Aug. 1915, in the' general retreat after the fall of Warsaw.
The failure of the forts is due to several. causes: (1) Their location and details of con struction were known some yeal before the war, and guns were especially designed to de stroy them. (2) Their armament was not up to date and, therefore, easily overpowered by the latest types of guns, the existence of which was unknown to the defense. 0) The garri sons permitted the enemy to emplace his guns within effective range, but beyond the range of the guns of the defense. (4) The advantage of concealment as a defensive measure is il lustrated by the operations againk Ossowetz. (5) The advantage of keeping the enemy at a distance is illustrated by the operations around Verdun and Nancy.
The experiences of the European War con firm the conclusion reached during the siege of Port Arthur in 1904, that the mounting of large-calibre guns in a fort for use against i siege guns of the enemy is a fatal error.
A modern fortress should consist of a large area, so organized as to ensure extreme mobility to troops and guns. Concealment is all im portant. Permanent gun emplacements should' therefore be constructed. only at important, i points .with the primary intention of delaying the enemy in bringing up his heaviest siege, guns, The main reliance should be placed upon mobile guns, some of which should be at, least as powerful as any which the enemy cap bring up. These,roobile guns should be located, in earthen: emplacements,, wyll conceale4 flora hostile observation. Unless the garrison is strong enough in both mobile troops and mobile guns to prevent the enemy from coming within effective range of his objective, then there is no hope of offering a prolonged resist ance. Consequently, entrenched areas with mobile troops and mobile guns are a more de pendable protection than a stereotyped system of permanent forts.
Permanent Fortifications.— The tendency to dissemination in permanent fortifications began in 1885, after experiments by Van Sauer and Mangin, who demonstrated the effect of high explosive shells and advocated very small armored forts. From these experiments and
those of other French officers arose the system of small, isolated forts, heavily armored and united by a belt line railroad, on which ran against assault. (4) Disposition such that, if the enemy occupies part of the line, he cannot maintain himself against counter attack.
These conditions are obtained by successive lines and a development of the front to the maximum permitted by the terrain. There should be a first line of continuous trench en barbette, supported by small armored forts all in front of the main lines, consisting of small works for rapid fire and heavy guns under cover of a heavy mass of concrete, in rear of which another defiladed line of the same char acter covers the intervals and supports the works in front. The gorge is closed and the entrance is through a subterranean passage.
Forbenius believes that the fortified places that have been captured during the European war may be placed in three groups — those trucks carrying heavy guns. Later this system was adopted by the Germans at Metz.
Colonel Voelki bases his calculations on a firm belief that it is not necessary greatly to increase defensive means; contending that analogous conditions obtain for the attack and defense; and that small forts with movable heavy artillery form a correct defense. This principle relies upon the small size of targets and the consequent difficulty of hitting and destroying them; and thus discards the idea of utilizing heavy centres of passive resistance except when absolutely unavoidable.
A typical work should fulfil the following conditions: (1) Efficacious fire against the attack until the last moment. (2) Support to neighboring works with defiladed guns under cover to sweep the intervals. (3) Protection that capitulated after a brief bombardment, those that were evacuated without resistance and those that surrendered after a siege of 7 to 12 days. The first were taken by storm on account principally of the superiority of the attacking artillery, which occupied good posi tions and fired effectively on visible and well defined targets without interference. The second group, although abandoned without re sisting, would have suffered the same fate had they held out; while the third suffered from lack of offensive initiative on the part of the garrisons, though also in these cases the artil lery preponderance greatly favored the Ger mans. Others, such as Toul, Verdun and Bel fort, have survived because the mobile armies have co-operated in their defense by taking advantage of all the accidents of the terrain to construct advanced lines, such as above out lined. Still others, such as Paris, Przemysl, Cracow and Koenigsberg, have assisted the field armies with their garrisons.