by J E Kauffman
During the final construction phase in the 1890s, additional renovations took place, but not in all the forts. The most significant was the introduction of reinforced concrete that owed its increased strength to the addition of metal bars. In general, the concrete was poured over rebars (steel bars or rods) linked together to form a grid. Reinforced concrete was used in the newest forts and only in additions to the older ones. A number of the older forts built before 1890 included caponiers – casemates extending into the fossé that included weapons positions to cover the length of the fossé to prevent the enemy from crossing. Masonry caponiers in the flanks or in the frontal sections of the fossé were exposed to direct enemy artillery fire, which could have ruinous effects, especially after the advent of the high-explosive shell in the 1880s. Thus, they were removed from many of the modernized forts. Gorge caponiers, however, often remained because they were not overly exposed. In many forts, caponiers were replaced with counterscarp casemates of reinforced concrete, or, in rare instances, only of concrete. Subterranean passages beneath the moat, usually of reinforced concrete, linked the coffres to the fort.
When the high-explosive shell appeared, it was deemed necessary to test its effects on forts. These experiments showed that the traditional fossé with high scarp walls was vulnerable. The solution was to demolish the scarp wall or greatly reduce its height, except in the gorge. Thus, in the new or renovated forts a gentle earth slope rose to the ramparts from the floor of the fossé or a low scarp wall. Since the ramparts had to be moved back in order to achieve the gentle slope, the size of the area enclosed by the ramparts was reduced. The counterscarp in the gorge remained vertical. This concept removed the rearward scarp walls from the direct line of enemy plunging artillery fire. A protective concrete slab was added over the top of a number of masonry counterscarp walls. The layer of earth was removed from the area behind the counterscarps (against the glacis) and was replaced with rocks to prevent artillery fire from penetrating the glacis. The fortification engineers recommended building concrete counterscarp walls in the new forts, but few were actually built. The older forts that formed the inner ring were seldom modernized. In 1906, Fort Chanot at Toul was converted from an ouvrage (see below) into a fort with concrete scarps and counterscarps. At the old fort of Tillot, also at Toul, two counterscarp walls were changed to concrete when its caponiers were replaced with counterscarp coffres during the first decade of the twentieth century. At Fort Uxegney at Épinal, two counterscarp walls were changed to concrete a few years before the war. At Belfort, the new Ouvrage of Meroux was built with concrete counterscarp walls.27 Lieutenant Colonel Philippe Truttmann points out that early in the twentieth century the French army decided that replacing the scarp walls with a gentle slope was more economical, but it was not as effective as building concrete walls.* The war proved how ineffectual the earthen layer was, especially in the modernized ouvrages.28
Examples of ouvrages, coffre and triangular profile.
In the late 1880s, the army engineers introduced new and smaller positions called ouvrages (works) or redoubts between the forts for the infantry. They mostly filled gaps between forts in a ring and often served as advanced positions. Many were little more than shelters or field fortifications. In the early twentieth century, a number of these positions were modified. Known as modernized ouvrages, they were similar to new ouvrages built at that time. These improved ouvrages took on the appearance of a small fort with a fossé, a small caserne and often included armoured weapons positions. The older infantry ouvrages usually consisted only of a large abri (in this case for the troops) or a small caserne and a fighting position. In addition, mainly in the early 1900s, a number of concrete infantry abri were built to defend gaps between forts. A number of individual battery positions, some rather simple positions with an abri, others much like an ouvrage with a fossé, completed the inventory. The larger of these ouvrages, whether for infantry or artillery, presented a ‘triangular profile’. In these ouvrages, the masonry counterscarp wall was 2.5m to 3m high and there was no scarp wall. With few exceptions, there were no coffres in the counterscarp to defend the fossé. The reason for this is that the outline of most of these ouvrages was oval, often bean-shaped so that most of the fossé sections were curved. In this arrangement, the fossé could only be defended from the ramparts. To make matters worse, repeated hits by artillery against the gentle slope between the base of the fossé and the ramparts tended to crumble the earthen slope causing sections to slide into floor of the fossé filling it so completely that the Germans were not even aware that they were crossing a moat. The French began to correct the problem in some of the last forts and ouvrages they built such as Fort Vacherauville (Verdun) and Fort Chanot (Toul) as they returned to vertical scarp walls. In the 1890s, barbed wire was introduced, mostly in fortifications without a scarp wall, but it was of little value if the earth of the sloped scarp filled the fossé after a bombardment. During the same period, the French also used a grille, a fence about 4m in height and surmounted with spiked bars set in concrete along the base of the fossé where the scarp wall would have been. The grille could also cover other vulnerable sections of the fortifications. Several forts had a drawbridge entrance located between the counterscarp wall and the scarp in the gorge with the wartime entry beneath the ditch.
The few combat abris built in 1913 were made of all reinforced concrete and latrines were inside. In some cases an escape tunnel was created in the cistern. They were company sized (for 200 men) with 4 large rooms and 3 outside latrines. Half-company size abris had only two large rooms and 2 outside latrines. Abris were spaced in intervals and behind forts and usually included infantry field works including concrete trenches.
Two French combat abris between the Meuse and Froideterre (MF).
The forts’ main purpose was to form strongpoints to deny access to the enemy. For this reason, they needed defensive weapons to repel an assault before it reached the fort and to throw back the enemy if they succeeded in penetrating into the fossé or beyond. Thus, the first forts built in the 1870s were provided with caponiers (casemates in the fossé) armed with machine guns and/or rapid-firing small cannon. Later, the caponiers were replaced with coffres equipped with similar weapons that covered the fossé from the counterscarp. The advantage of infantry positions on the ramparts was that they could cover the fossé and the glacis simultaneously. The forts required heavier armament that could not only defend the fort but also act as an offensive weapon against enemy troops trying to pass between gaps in the fortress ring or preparing to assault the fort. For this purpose, artillery of various sizes was emplaced on the fort. Mounting artillery in masonry casemates became inadequate during the period of the American Civil War when rifled artillery turned walls into rubble. As with the French built forts in the 1870s, the only satisfactory solution had been to replace the walled fort with an earth-covered masonry fort.29 The artillery of these forts was mounted in open positions behind the ramparts with traverses separating the positions. If the enemy hit one gun position, the traverses protected the adjacent emplacements from the effects of an explosion. Masonry abris were built into the traverses to shelter artillery or troops. The army found this arrangement satisfactory until the high-explosive shell appeared on the scene in the 1880s. ‘Torpedo shells’ threatened not only the integrity of the earth-covered masonry of the forts, but also their artillery. In the 1870s, Captain Henri Mougin and other French fortification engineers worked on armoured casemate designs for the main-line forts.30 The first specimens were expensive and usually housed only one gun of up to 155mm calibre. At Battery Éperon in the Charmes Gap two Mougin armoured casemates Mle 1878 for a 155mm gun were installed. Mle 1878 casemates for a 138mm gun were placed at Fort Parmont and Fort Château Lambert on the Moselle Heights.31 The French army, however, was not fully satisfied with these armoured casemates. The best alternative appeared to be the armoured turret. Mougin was the first to develop one for the French fortifications in the 1870s. The army o
rdered several of these turrets for the land forts, but tests in the 1880s showed that they did not withstand the high-explosive shells. Thus, army engineers in Europe continued to search for another solution.
Armoured casemates, nonetheless, turned out to be valuable in coastal defences. A new type of artillery mechanism, the disappearing gun, was also a boon for coastal fortifications since it could be loaded before it was raised above the parapet to fire. The recoil brought the gun back into the loading position below the rampart. In some countries, they were adopted for land defences, especially in mountain positions.32 In the 1890s, the search continued for a better and more effective armoured turret. Captain Alfred Galopin designed a turret for a pair of 155mm L (long barrel) guns and later, a similar retracting turret for a single gun 155mm R (short barrel), which was adopted by the army.33 This turret began to appear in forts during the first decade of the twentieth century. In 1901, the army also approved a retracting turret with two rapid-firing 75mm guns designed in 1897. This turret and the single 155mm gun turret became the main offensive weapons in most French forts. For protection, a machine-gun turret, designated GF4, also went into production early in the century. Since the forts also needed ‘eyes’ to direct the fire of the artillery turrets, positions were added on the forts for armoured domes (cloches) of three types (Type 1 Mle 1892, Type 2 Mle 1901 and Type 3 Mle 1912).34 They held one observer who usually communicated with a command centre or turret block by means of acoustic voice tubes. Smaller observatories for lookouts, often set in a concrete block in the ramparts and protected by an armoured door, were added in 1902.
Siege Artillery
The belligerents required siege artillery to smash trench lines and to destroy forts. The French only used it against their own forts, which had been captured by the Germans. The Germans equipped their field artillery with howitzers, which gave them a tremendous advantage over the French in open as well as trench warfare, but they also produced siege artillery in preparation for breaking the Belgian and French fortress lines created in the 1880s and later. In the 1890s, the German army worked with the Krupp Company to develop the heavy 305mm Mörser which was designated a coastal weapon to disguise its actual purpose. The army had nine of these weapons by 1906. Afraid the Mörser would not be able to destroy the French forts, the Germans developed a newer weapon, which was ready by 1909, had a range of up to 12,000m and had greater penetrating power. Since the 305mm Beta-Gerät 09 howitzer was heavier than the 305mm Mörser, it was more difficult to move. There were eight of these mortars in four two-gun batteries and the two howitzers in one battery when the war began. These weapons required a number of train cars to move their components. The Krupp 420mm Gamma gun, developed after 1906, entered military service in 1911. This monster required more preparation and work to install than the older guns did. It was also more difficult to move than the 305mm weapons. These fort busters were in service in two two-gun batteries by 1914 and a fifth howitzer went into reserve. Krupp produced five more of these weapons and a number of spare barrels during the war. An armoured cab added to the Gamma guns in 1916 protected the gun crews from French counter-battery fire, which was becoming increasingly effective. In 1911, Krupp designed a lighter wheeled version of the 420mm Gamma gun which was slightly more mobile and of a different design to the 1906 version. The gun had to be disassembled before it could be transported beyond a short distance. Only two were ready when the war began, but by the time of the Battle of Verdun, in 1916, six more had entered service.
Several types of German Heavy Artillery.
When the war began, Germany had five batteries with two 305mm weapons, a one-gun battery with a single wheeled 305mm Beta and another battery with a wheeled 240mm L/12. The army also had two batteries with two 420mm Gammas each and a battery with two 420mm Big Berthas. In October 1914, a one-gun Gamma battery was added. When operations on the Eastern Front started in 1915, two additional two-gun Big Bertha batteries and a single-gun battery with a wheeled 280mm L/14 were ready. In 1916, a few more batteries with seven additional Big Berthas, three Gamma guns and four 305mm mortars were added. As the year and the Battle of Verdun drew to a close there was little need for fort busters.
The Austrians were the only other major power on the Continent with new heavy siege artillery. While the Germans worked on the 420mm weapons several years into the new century, the Austrians had their Skoda factories working on similar weapons. They developed the 305mm M.11 (1911) mortar. It was lighter than the older German 305mm mortar and had a greater range. The Austrians sent eight of these, with crews, to aid the Germans when the war began. The Skoda company designed 420mm howitzers for coastal defence in 1914. The army placed one of these 209.9-ton turret mounted weapons at a coastal fort protecting Pola and others followed. In 1916, the high command decided to move these 420mm howitzers from the coastal defences and make them mobile. This led to the designation of 420mm M.16. Including the two 420mm M.14s, Skoda produced a total of eight during the war. One of these survived the war, and took part in the bombardment of a Maginot Line fort in the Second World War when the French mistook it for a Big Bertha. The first two 380mm M.16 howitzers were ready in time for an offensive on the Italian Front in 1916. These guns had a longer range than most siege weapons and proved effective in blasting away at Italian mountain fortresses.
The Austrian siege guns were mostly motorized giving them more flexibility than their German counterparts, which relied heavily on railways. When the war broke out, the Austrians had twenty-four 305mm M.11 mortars, all motorized, in fifteen batteries. In 1915, they added five more two-gun batteries of M.11s. Between 1915 and 1917, the Austrians received seven additional 420mm howitzers and two 380mm howitzers, which they assigned to fortress artillery units with more 380mm howitzers under construction.
Table 3: Comparison of Heavy Artillery
Another significant addition, the Casemate de Bourges – named after the test ground where it was developed, was adopted in 1899. The first was built for a pair of 95mm guns; others were redesigned to take two 75mm guns on a special mount. In addition to the gun chamber, the reinforced concrete structure included an observation position, a magazine for 500 rounds below the guns and a work/rest area for the 19-man crew. These casemates faced a flank of the fort so that, even though their maximum wall thickness was only about .8m, their angled design kept them out of the direct line of fire of heavy enemy artillery. Their guns covered the gap between them and the next fortification with flanking fire.
The main types of turrets found at Verdun.
Electrical power was added to many forts for lighting and operating the ventilation system and the turrets. Until the late nineteenth century, the fumes generated by the firing weapons were expelled through a small window-like vent above the gun embrasure.35 Between 1904 and 1914, the French installed ventilation systems in a number of their forts. Hand-operated systems were put in at thirteen forts at Verdun: Haudainville, Froideterre, Moulainville, La Falouse, Dugny, Déramé, Landrecourt, Regret, Sartelles, Choisel, Borrus, Charme and Rozellier. An electrical ventilation system was installed at Vacherauville between 1912 and 1914, while work on a similar system in 1914 only began at Douaumont and stopped when the war began. At Toul, twelve forts received manual ventilation systems (Bouvron, Bruley, Chanot, Domgermain, Écrouves, Est Vieux Canton, Francheville, Gondreville, Mordant, Tillot and Trondes). Between 1910 and 1914, ventilation systems were installed at Vieux Canton, Villey le Sec, Blénod and Lucey, including in the turrets. At Épinal electric ventilation systems went into forts Arches, Dogneville, Longchamp, Adelphes and Uxegney, while at Belfort they were installed at Bois d’Oye, Chèvremont, Côte d’Essert, Fougerais and Salbert. Manual ventilation was set up at Fort Frouard in the Charmes Gap in 1910 and electrical systems at forts Manonviller and Pont Saint-Vincent. The forts of the Meuse Heights did not undergo any of these improvements,
Examples of machine-gun turrets and Mougin turret for 155mm guns. (Photographs of Villey le Sac by Bernard Lowry a
nd others by the author). Observation cloche. Pamart cloche for machine gun, also known as ‘Elephant Head’, were added to some forts in 1917. Turret at Fort Vaux destroyed by Germans during their retreat. (Photograph by Clayton Donnell)
