by J E Kauffman
During the second half of the nineteenth century, turret armour kept pace with changes in fortifications. The Grüson works in Germany developed a secret method that gave them the edge in the industry for many years. In 1878, the French armour commission concluded that the steel in use shattered under excessive shock. The commission next considered either rolled iron or cast iron, which is not as malleable as wrought iron.11 As wrought-iron plates increased in size, a process was developed to weld them together. The problem with the welding method, however, was that it had a tendency to split along the seams when it was hit. The commission decided to adopt both rolled iron and the less expensive hard cast iron. Hard cast iron is rigid, could break up the heaviest projectiles of the 1870s and lends itself to the creation of rounded surfaces. Rolled iron, on the other hand, is easier to shape and can reach required thicknesses.12 In the early 1880s, carbon was added to steel to form a stronger metal. The addition of tungsten and chrome greatly increased the overall strength of steel.
The new high-explosive shells were made of steel, which gave them greater capabilities and volume. At St Chamond in 1884, tests showed that rolled iron armour was more resistant than hard cast iron to these steel shells. The Mougin turrets, made of hard cast iron, had already been installed when tests revealed that they were inadequate. The commission selected rolled iron for armour. The Mougin turret was rather flat at the top, but the Bucharest tests demonstrated that curved roofs were preferable for turrets. The commission also concluded that in the future it should strive to obtain eclipsing turrets, which meant that the guns could not extend beyond the embrasure. After tests at Chalons in 1887–8, the commission adopted two Mougin retracting turrets.
The commission also tested a couple of non-eclipsing turrets at Chalons. They rejected a St Chamond turret, very similar to the Mougin, but with gun embrasures closer to ground level and a laminated curved armoured dome instead of a cast-iron one. This experimental turret was installed at Fort St Michel (Toul). The Montluçon turret also had a curved dome but its gun embrasures for 155mm C (howitzers) were cut into its dome. This turret served as a detached armoured battery near Fort Lucey (Toul). The Bussière and Souriau turrets were among the first eclipsing turrets produced in France, but neither proved satisfactory. In addition, the price was up to four times higher than the noneclipsing type. The Bussière eclipsing turret had a roof of rolled iron bolted to the turret sides. It mounted a pair of 155mm L guns and, like other turrets, included hydraulic brakes. Manoeuvring the turret required a steam engine. Its main weakness, concluded the commission, was its fragile operating system. The mixed metal armour of the turret’s flat roof was .24m thick and consisted of two plates screwed together. The turret walls were .45m thick. The diameter of the turret was 5.25m. This turret was mounted next to Fort Souville (Verdun).
Colonel Souriau designed one of the most interesting turrets at the Schneider factory. His eclipsing turret mounted two 155mm L guns under a curved roof. His unique eclipsing system had the turret’s vertical movement relying on a platform floating on water in a tank. However, the commission considered this system a liability due to the fact that water and metal would be in contact.
In 1892, Captain Galopin was assigned to study Mougin’s new version of an oscillating turret which had gun embrasures pointed below the level of the glacis armour right after firing then tilted back up to the battery position. Galopin’s own design was tested shortly afterward. His turret’s eclipsing movement used counterweights and shifted from the battery (firing) to the concealed position in 2 seconds.13 After the guns were loaded, the turret was raised and its weapons were aimed and fired in 4.5 seconds. The turret required a crew of six men in the turret and eleven in the block below the turret. The Galopin turret mounted two 155mm L cannons and the roof comprised 30cm of rolled iron lined with sheet metal. The sidewalls were made of 45cm-thick half-hard steel. The turret, 5.5m in diameter, included ventilators and a monte-charge for moving the ammunition. Fort Arches (Toul) received one of these turrets and three blocking forts (forts d’arrêt) of the Charmes Gap had five.
In 1903, the army engineer section redesigned the Galopin turret into a small single-gun turret with steel armour 30cm thick. The firing chamber weighed 70 tons (10 tons less than the two-gun turret). It housed a 155mm R (short barrel) gun with a range of 7,200m as opposed to the 155mm L that had a range of 7,500m. It had the same features as the larger turret, but the few modifications made it more affordable.14 In a few years, it was adopted as the Galopin 155mm R Mle 1907 turret. By 1914, twelve of these turrets were emplaced.15
Bussière designed an eclipsing turret for two Nordenfeld 57mm guns in 1893. This may have been in response to a similarly armed Grüson turret and a mobile model that had grown in popularity. Although the French army purchased four of these turrets, it did not seem to be a good investment since it only mounted a small calibre gun. They were installed in three forts in the mid-1890s. The army modified two of the turrets in 1909 and replaced the 57mm guns with 75mm guns: one at the Ouvrage of Bouvron and the other at the Ouvrage of Est du Vieux Canton. The two turrets at Fort Manonviller were modified.
By the end of the nineteenth century, the 75mm guns became prevalent not only in field artillery but also in fort artillery, before the army converted the two 57mm gun turrets. Using the Galopin turrets as a basis for a new turret design, the French engineers developed a turret mounting two 75mm R (short barrel) guns. Although it was adopted in 1902, this new turret is usually identified as a Mle 1905. Some sources refer to it as Mle 1903. The turret roof armour was 35cm thick and the walls 25cm. It was installed in a combat block with the counterweights and balancer (in the lower level of the block) for eclipsing. Command and control occupied the intermediate level and the firing chamber in the turret was at the upper level. A manual ventilator in the turret removed escaping fumes from the guns. In 1912, ventilators were installed in some of the older turrets as well.16 The steel roof armour was 30cm thick and the mantle 15cm.17 Between 1903 and 1914, fifty-five of the seventy-three turrets of this type were emplaced on the main line and in other locations, including in coastal defences. The majority of these turrets went to the fortresses of Verdun (fourteen), Toul (eighteen) and Belfort (ten). Only four went to the forts at Épinal. Like a few of the old Mougin turrets, several of the Mle 1905 turrets remained in service until 1940 in the Maginot Line.
Before long it was decided that machine-gun turrets were needed to protect the fort. The Puteaux armaments work designed the first turret, the GF3 (Gatling Fusil) Mle 1895. It was lightly armoured with 12cm of rolled iron for the roof, and steel sides only 1.5cm thick.18 There was one of these turrets at Fort Manonviller. When the more effective Hotckhiss Mle 1899 was perfected, the GF4 turret with a thicker roof and side armour was designed. Its side armour was thick enough to resist infantry weapons because the turret rose to the firing position after the enemy bombardment stopped in order to meet an infantry assault. The roof was thick enough to resist 155mm artillery rounds. The turret mounted two Hotchkiss 8mm machine guns, but the gunner did not fire them simultaneously. One man occupied the turret, firing the machine gun and directing movements. Another man stood nearby handing him ammunition clips for the machine guns. In 1914, eighty-seven of these turrets were installed, mostly in the forts of the main line.
The 155mm C (howitzer) Turret Mle 1908 was a late development. It was a non-retracting, single-weapon turret with a steel dome 30cm thick. Only two were installed in 1914, both at Fort Longchamp. There were plans to install two a short distance behind Fort Douaumont in 1914, but construction had to halt in August of that year.
In addition to the turrets, the army ordered a number of armoured observatories. These fixed turrets, called cloche, were constructed with steel about 25cm thick. They usually had three narrow observation crenels and were equipped with instruments to observe artillery fire. They often occupied positions near a gun turret.
Comparison of fortresses on the Eastern and Western fronts.
Both maps are the same scale.
Of the major European powers, Russia had had the most recent experience in large-scale trench warfare. In 1904, during the Russo-Japanese War, Russian troops built defences approximately 80km (50 miles) long to hold Liaoyang. In 1905, they built about 160km (100 miles) of lines at Mukden. Despite these efforts, they ended up losing the battles that ensued. The line between Kovno and Novogeorgievsk, which covered over 320km (200 miles), was almost 100km longer than the French line between Belfort and Verdun and lacked major fortresses. The front between Novogeorgievsk along the Vistula extended for 160km (100 miles), but had only two fortresses. Along the Galician frontier, there was an additional 350km or more without fortresses. The river lines on these three fronts formed the main barrier for Russia. On the central front on the Polish plain, there were few barriers except for the wide Vistula and the Bug River further to the east. Even after the fiasco in the Russo-Japanese War, the Russian leadership still failed to grasp the requirements of trench warfare and paid little attention to defensive operations, especially after the 1909 directive.
The German fortresses, among the most modern of the era, saw almost no action during the war, whereas the French, Belgian, Austrian, Italian and Russian fortifications were heavily involved in combat. Before the war, the Germans and Austrians, mostly focused on eliminating enemy fortresses, strove to develop heavy artillery like howitzers of 305mm and 420mm. They also manufactured short-range mortars (minewerfer) to tackle not only the enemy forts, but also the trenches they expected to encounter between forts. Before the war, the Germanic allies did not try to create a continuous defensive line on the Eastern and Western fronts. Germany’s key fortified positions at Metz–Thionville and Strasbourg–Mutzig were designed to deny key strategic points to the enemy and relied on the Vosges and on other natural obstacles to channel a French advance. The Germans applied the same principles on their eastern border where a small number of fortresses relied on the wooded lake region of East Prussia to support a defensive action. The Austrians, on the other hand, built only a couple of fortresses on the Galician Front in the Carpathian Mountains to blunt an enemy advance if Galicia was lost. Along the Alpine front with Italy, the mountains formed the main obstacle and several forts effectively guarded the passes.
Examples of Russian and Belgian forts. The Belgian forts were much weaker than the French, and not made of reinforced concrete.
The Belgians had turned Liège, Namur and Antwerp into fortresses. They did not even try to create a continuous line. They intended to dig trenches to defend the intervals between the forts of each ring and wait for their allies to manoeuvre between them. Allowing a fortress to be isolated proved to be a bad idea during the First World War. Originally, Brialmont had built the Belgian forts of Liège and Namur with concrete that was not continuously poured, which weakened the structure. The Achilles heel of the Brialmont forts was that they had not been strengthened with reinforced concrete. Like the French and German forts, and unlike the Russian ones, they had armoured components, including gun turrets. Although their armour was intended to resist 210mm calibre guns, it failed to do so and it was no match for the 305mm and 420mm monsters that tore the forts apart. The catastrophe that befell the Belgian forts almost became a disaster for the French because Joffre and many of his fellow officers concluded their own forts must be equally vulnerable. Joffre took advantage of the situation to remove what artillery and ammunition he could from his forts in August 1915 to make up for the deficiencies in his field artillery. In 1916, the French discovered they had been mistaken about the worth of their forts.
The Fortress Line
The French had to protect their new border after the Franco-Prussian War of 1870–1. This task fell to General Raymond Adolphe Séré de Rivières who became Director of Engineer Services at the War Ministry in February 1874.19 He developed plans for France’s new defensive lines and the old fortress of Verdun fit into this new scheme. Work began on the first of six detached forts, which later formed the inner ring, within a year of the Prussian (German) evacuation of Verdun in September 1873.20 These fortifications became known as the ‘Forts de Panique’. At the same time during the 1870s, construction started on another ring of six detached forts, mostly on the right bank of the Meuse. In 1881, the outer ring was expanded with the construction of Fort Vaux and two other forts. Between 1883 and 1885, Fort Moulainville and five more fortifications were added. Fort Douaumont was one of the last masonry forts, begun in 1885.
The new line of fortifications was to consist of four fortress rings spanning the length of the new border region with Germany. Séré de Rivières established four fortresses, also known as entrenched camps (Camps Retranchés), each with a ring of forts around it.21 The French army engineers worked on other fortresses as well. However, these fortifications were relegated to second or third class status by the end of the nineteenth century.22 Séré de Rivières had to come up with new fort designs at a time when innovations in artillery came rapidly and rendered many fortifications obsolete almost as soon as they were built.
The period between September 1873 and the late 1880s was dedicated to the building of fortifications in France. Construction started simultaneously on the fortress rings of Toul, Épinal, Belfort and Verdun. In addition to these emerging fortress rings, the French built several forts on the Meuse Heights between Verdun and Toul, in the Charmes Gap between Toul and Épinal, the Moselle Heights between Épinal and Belfort, and the Belfort Gap. The French army established a fortified zone that extended from Verdun to Toul and from Épinal to Belfort and anchored each end of these sections with a fortress. The forts occupying positions in the Charmes Gap served as forts d’arrêt that dominated key points from which they were to hinder or actually ‘stop’, as their name implies, the enemy’s advance. The individual forts along the Meuse and Moselle Heights, linking Toul to Verdun, and Épinal to Belfort, were not forts d’arrêt.23 They were, in fact, part of a line linking each pair of fortresses. Leaving the Charmes Gap lightly defended was not a serious problem because a large section of this gap faced the Vosges Mountains, which formed a natural barrier. The Germans would have to advance from a direction leading towards Nancy where the forts d’arrêt would block the main routes. The French military thought that they could easily rout a German force channelled through this gap. The first two French war plans were exclusively defensive and concentrated on holding the main positions and on counter-attacking against any point through which the enemy advanced.24 The French command, like its German counterpart, planned to mobilize an army that could defend massive swathes of territory and would not allow the enemy to penetrate deep into their territory along the Franco-German border.
Fortified cites and main railways on Franco–German border.
Map of Verdun Fortress area.
The year 1886 brought, according to the French, the ‘Crisis of the Torpedo Shell’. A new type of shell, named for its cylindrical shape and filled with a high explosive known as melinite, was perfected. This high-explosive shell was made of steel instead of cast iron, had an overall weight that allowed it to carry almost eight times more explosive and achieved a greater range than other projectiles of the period. In that year the French tested the new shells by firing over 242 rounds from a 155mm Mle 1877 cannon and a 220mm mortar Mle 1880 on Fort Malmaison (1878–83) at Laon. The result was extensive damage to the scarps, counterscarps, facades, armoured sections, artillery positions on the ramparts and the interior of the brick structures. The experiment demonstrated that the new high explosive had rendered masonry forts obsolete. The French needed to come up with a new solution quickly. Belgian General Brialmont thought he had already found one before he began to build his new forts in July 1888. He used concrete and designed his forts to resist artillery rounds of up to 210mm.
The crisis of the high-explosive shell ended the first phase of fortification construction that had begun in 1874. During a second phase that lasted through the remainder of the 1880s, entire
sections of existing fortifications were reinforced with concrete. In France, priority was given to strengthening the masonry forts that had barely been completed and included Verdun and the other fortress rings rather than building new concrete positions. To achieve this the military engineers cleared the earthen cover from the roofs of important structures within the forts before pouring a layer of concrete about 2.5m thick. They finished the job by recovering the structures with earth. This new roof or carapace was up to 4m thick. They also covered exposed masonry walls with a concrete layer about 1.5m thick, and reinforced counterscarp walls with concrete at a few locations. After 1887, the new forts they designed were mostly made of concrete. Nothing was done to strengthen five of the twelve forts built during the 1870s at Verdun. However, of the ten that were built before 1886, all but two were reinforced with concrete. Similar arrangements took place in the other three major fortress rings. This second phase represents the first period of modernization.
The third and final construction phase began in 1892 and lasted until the war. As progress continued to be made in the development of artillery, the fortress engineers met the challenge by rebuilding parts of some of the fortifications with reinforced concrete. By the end of the decade, they added armoured positions of steel. In 1906, construction began on a generation of a few state-of-the-art forts. The French experimented with different types of concrete for their fortifications until they hit upon the right mixture of cement and aggregate for the greatest strength. They called it béton spécial (special concrete) and used it to reinforce fortifications during the second and third phases between 1888 and 1914.25
Once more, the area above the roofs were cleared, a cushion of sand was added and a layer of special concrete was poured to serve as a bursting layer after a shell penetrated the earthen layer above it. In some cases, the masonry roof had to be replaced with a concrete one. The caserne (barracks area that often included the large dormitories with bunks, kitchen, latrines, stores and other facilities) and magazines were covered with a layer of special concrete that often formed a shell over the structure. The facilities of the caserne were typically clustered together and usually occupied a large rectangular area of the fort. Often, the side of these casernes facing the rear ditch of the fort was exposed. The rear side of a ditch or moat (fossé) is known as the gorge. When the caserne had an exposed side facing the gorge, the latter often served as a courtyard. In some cases, the caserne opened onto a courtyard within the fort, while in others, a courtyard was located in the centre of the caserne. Forts built before 1887 often had large vaulted openings that allowed natural lighting. When the reinforcement was added, the exposed side of the caserne had to be covered with concrete leaving smaller entrance openings. Alternately, a new concrete wall was built in front of the original masonry wall, leaving a corridor between the two. Either way, natural lighting was greatly reduced. In some cases, part of the caserne was reinforced with a concrete shell and served as a wartime facility while the remainder of the masonry structure was used in peacetime. On the ramparts, masonry shelters (abris) of various types such as infantry or traverse abris were often given concrete protection.26 Many of the entrances remained unprotected, except by an earthen cover, since they faced away from direct enemy fire.