Polygonal fort
A polygonal fort is a type of fortification originating in France in the late 18th century and fully developed in Germany in the first half of the 19th century. Unlike earlier forts, polygonal forts had no bastions, which had proved to be vulnerable. As part of ring fortresses, polygonal forts were generally arranged in a ring around the place they were intended to protect, so that each fort could support its neighbours. The concept of the polygonal fort proved to be adaptable to improvements in the artillery which might be used against them, and they continued to be built and rebuilt well into the 20th century.
Bastion system deficiencies
The
Other European engineers quickly adopted the three-parallel Vauban system, which became the standard method and would prove to be almost infallible.[2] Vauban designed three systems of fortification, each having a more elaborate system of outworks, which were intended to prevent the besiegers from enfilading the bastions. During the next century, other engineers tried and failed to perfect the bastion system to nullify the Vauban type of attack.[3] During the 18th century, it was found that the continuous enceinte, or main defensive enclosure of a bastion fortress, could not be made large enough to accommodate the enormous field armies which were increasingly being employed in Europe; neither could the defences be constructed far enough away from the fortress town to protect the inhabitants from bombardment by the besiegers, the range of whose guns was steadily increasing as better manufactured weapons were introduced.[4][5]
Theories of Montalembert and Carnot
Marc René, marquis de Montalembert (1714–1800) envisaged a system to prevent an opponent from establishing their parallel entrenchments by an overwhelming artillery barrage from a large number of guns, which were to be protected from return fire. The elements of his system were the replacement of bastions with tenailles, resulting in a defensive line with a zigzag plan, allowing for the maximum number of guns to be brought to bear and the provision of gun towers or redoubts (small forts), forward of the main line, each mounting a powerful artillery battery. All the guns were to be mounted in multi-storey masonry casemates, vaulted chambers built into the ramparts of the forts. Defence of the ditches was to be by caponiers, covered galleries projecting into the ditch with numerous loopholes for small arms, compensating for the loss of the bastions with their flanking fire.[6] Montalembert argued that the three elements, would provide long-range offensive fire from the casemated main curtain, defence in depth from the detached forts or towers and close-in defence from the caponiers.[7] Montalembert described his theories in an eleven-volume work called La Fortification Perpendiculaire, which was published in Paris between 1776 and 1778.[6] He summarised the benefits of his system thus; "...all is exposed to the fire of the besieged, which is everywhere superior to that of the besieger, and the latter cannot advance a step without being hit from all sides".[8]
A full realisation of Montalembert's ambitious plans for a great inland fortress was never attempted. Almost immediately after publication, unofficial translations into German were being made of Montalembert's work and were being circulated amongst the officers of the
Despite the conservatism of the French engineer corps, two French engineers experimented on a modest scale with Montalembert's ideas for detached forts. Jean Le Michaud d'Arçon, ironically one of Montalembert's detractors, designed and built a number of lunettes (an outwork resembling a detached bastion) which were in accord with Montalembert's concepts. These lunettes were constructed at Mont-Dauphin, Besançon, Perpignan and other border fortresses, commencing in 1791 shortly before the Revolution. In the same year, Antoine Étienne de Tousard took up a position on Malta as an engineer to the Order of Saint John and was instructed to design a small fort to command the entrance to Marsamxett Harbour called Fort Tigné. Exactly how Tousard became acquainted with d'Arcon's lunette design is unknown, but the resemblance is too close to be coincidental. It was, like d'Arcon's works, quadrilateral in plan, divided by a traverse with a circular tower keep in the rear and the surrounding ditch was protected by counterscarp galleries. Fort Tigné, however, was a fully defensible and self-contained fort, larger and more sophisticated than d'Arcon's outworks,[10] and is regarded as being the first true polygonal fort.[11]
Montalembert's work was also allowed to take concrete form during his lifetime in the field of coastal fortification. In 1778, he was commissioned to build a fort on the Île-d'Aix, defending the port of Rochefort, Charente-Maritime. The outbreak of the Anglo-French War forced him hastily to build his casemated fort from wood but he was able to prove that his well-designed casemates were capable of operating without choking the gunners with smoke, one of the principal objections of his detractors.[12] The defences of the new naval base at Cherbourg were later constructed according to his system.[13] After seeing Montalembert's coastal forts, American engineer Jonathan Williams acquired a translation of his book and took it to the United States, where it inspired the Second and Third Systems of coastal fortification; the first fully developed example being Castle Williams in New York Harbor which was started in 1807.[14][15]
Prussian System
After the final fall of Napoleon I in 1815, the
The detached forts were polygons of four or five sides in plan, with the front faces of the rampart angled at 95°. The rear or gorge of the fort was closed with a masonry wall, sufficient to repel a surprise infantry attack but easily demolished by the defenders' artillery should the fort be captured by the attackers. In the centre of the gorge wall was a reduit or keep, provided with casemates for guns which could fire over the rampart or along the flanks to support the next forts in the chain.[21] The original bastioned enceintes of these fortresses were initially retained or even rebuilt so as to prevent an attacker from infiltrating between the outlying forts and taking the fortress by a coup de main. It was later thought by some engineers that a simple entrenchment would suffice or that no inner defence was necessary; the issue remained a debating point for some decades.[22] In any case, few European cities undergoing the rapid expansion caused by the Industrial Revolution would willingly accept the restriction to their growth caused by a continuous line of ramparts.[23] Aster insisted that his new technique was "not to be regarded... as a particular system" but this type of ring fortress became known as the Prussian System. Austrian engineers adopted a similar approach although differing in some details; the Prussian System and the Austrian System were together known as the German System.[24]
Lessons of the Crimean War
The Crimean War (October 1853 to February 1856) was fought by the
Impact of rifled artillery
The first rifled artillery designs were developed independently during the 1840s and 1850s by several engineers in Europe. These weapons offered greatly increased range, accuracy and penetrating power over smooth-bore guns then in use.[27] The first effective use of rifled guns was during the Second Italian War of Independence in 1859, when the French used them against the Austrians. The Austrians quickly realised that the outlying forts of their ring fortresses were now too close to prevent an enemy from bombarding a besieged town and at Verona, they added a second circle of forts, about 1 mi (1.6 km) forward of the existing ring.[28]
The British were apprehensive about a French invasion and in 1859 appointed the
In the United States, it had been decided at an early stage that it would be impractical to provide landward fortifications for rapidly expanding cities but a considerable investment had been made in seaward defences in the form of multi-tiered casemated batteries, originally based on Montalembert's designs. During the
In France the military establishment clung to the concept of the bastion system. Between 1841 and 1844, an immense bastioned trace, the
In the aftermath of defeat, the French belatedly adopted a version of the polygonal system in a huge programme of fortification which commenced in 1874, under the direction of General
The "torpedo-shell crisis"
From the mid-19th century, chemists produced the first
In France, the recently completed forts began to be refurbished, with thick layers of concrete reinforcing the ramparts and the roofs of magazines and accommodation spaces. The Belgians had not started their new fortifications when the effectiveness of the new munitions became known and their chief engineer, Henri Alexis Brialmont, was able to incorporate countermeasures in his design.[37] Brialmont forts were triangular in plan and made extensive use of concrete with the main armament mounted in rotating turrets connected by tunnels.[38] The French and Belgians assumed that the new forts must be able to withstand siege guns up to a calibre of 8 in (21 cm) as this was the largest mobile weapon in use.[39] In Germany, after updating their Bichler forts with layers of sand and concrete and building others in the style of Brialmont, a new design emerged, in which fort artillery and infantry positions would be dispersed in the landscape, connected only by trenches or tunnels and without a continuous enceinte. This type of fortified position was called a Feste and was the result of the work of several German theorists but came to fruition under Colmar Freiherr von der Goltz who was appointed Inspector-General of Fortifications in 1898.[40]
World Wars
First World War
At the start of the
On the Eastern Front, most polygonal fortifications were also quickly overcome by heavy artillery. The Kaunas Fortress (now in Lithuania) was the most expensive fortification in the Russian Empire, but a modernisation programme was incomplete. In July 1915, German assaults concentrated on three un-modernised forts in the southwest sector. Following the loss of these forts the garrison abandoned the entire fortress, prompted by the desertion of their commanding officer on the previous day, the assault having lasted only eleven days.[44] Another Russian ring fortress at Novogeorgievsk, later renamed Modlin, which guarded the northern approach to Warsaw, fell after a siege of 10 days in August 1915, with the loss of 90,000 men taken prisoner and 1,600 guns.[45] The largest Austro-Hungarian fortification was Przemyśl Fortress which protected the province of Eastern Galicia and had a ring of twenty five modern polygonal forts. An invading Russian army besieged the fortress, but initially lacked heavy artillery and were short of ammunition for their field guns. An initial infantry assault in September 1914 was repulsed with heavy Russian losses,[46] but the fortress was finally surrendered in the following March, after both a relief attempt and a breakout had failed.[47]
Following these failures, the French high command concluded that fixed fortifications were obsolete and they began the process of disarming their forts, since there was a grave shortage of medium artillery pieces in their field armies.[48] In February 1916, the Germans began the Battle of Verdun, hoping to force the French to squander their forces in costly counter-attacks in an effort to regain it. They found that the Verdun forts, which had been recently upgraded with extra layers of concrete and sand, were resistant to their heaviest shells. Fort Douaumont was captured, almost by accident, by a small party of Germans who climbed through an unattended embrasure, the rest of the forts could not permanently be subdued and the offensive was eventually called off in July after huge casualties on both sides.[49]
Inter-war developments
After the war, the apparent success of the Verdun forts led the French government to re-fortify the eastern border. Rather than build new polygonal forts, the method chosen was a developed version of the German Feste system of dispersed strongpoints connected by tunnels to a central underground barracks, all concealed in the landscape. This concept known to the French as fort palmé because the elements of the fort were analogous to the fingers of a hand.
Second World War
The war opened with the German invasion of Poland on 1 September 1939; by 13 September, Warsaw and the partly-modernised fortress of Modlin had been surrounded. The fortress was separated from Warsaw on 22 September and despite numerous German infantry assaults supported by heavy artillery and dive bombing, Modlin was not surrendered until 29 September after receiving the news that Warsaw had fallen.[53]
On 10 May 1940, German forces attacked the new Belgian forts, quickly
References
- ^ Hogg, pp. 51–52
- ^ Ostwald, p. 12
- ^ Duffy, p. 41
- ^ Royal Military Academy p. 143
- ^ Hogg p. 73
- ^ a b Wade, p. 110
- ^ Duffy p. 160
- ^ Lloyd & Marsh, p. 114
- ^ Duffy p. 163
- ^ Spiteri pp. 6-11
- ^ Spiteri p. 71
- ^ Lloyd & Marsh, pp. 125–127
- ^ Lepage p. 96
- ^ Wade p. 111
- ^ Hogg p. 78
- ^ Royal Military Academy pp. 127–128
- ^ Lepage pp. 147–148
- ^ Kaufmann & Kaufmann p. 7
- ^ Kaufmann & Kaufmann p. 9
- ^ Douglas, p. 126
- ^ Royal Military Academy pp. 132–133
- ^ Kenyon, p. 3
- ^ Lloyd, p. 98
- ^ Royal Military Academy p. 132
- ^ Hogg pp. 79–81
- ^ Hogg, pp. 80–82
- ^ Kinard, p. 222
- ^ Royal Military Academy, p. 150
- ^ Crick 2012, pp. 46–47
- ^ Dyer 2003, p. 7
- ^ Hogg, p. 101
- ^ Hogg, p. 102
- ^ Hogg, p. 104
- ^ Kaufmann & Kaufmann (Neutral States), p. xiii
- ^ Kaufmann & Kaufmann (Central States), p. 47
- ^ Donnel, pp. 7–8
- ^ Donnel, p. 8
- ^ Donnel, p. 12
- ^ Hogg, pp. 103–105
- ^ Kaufmann and Kaufmann (Central States), pp. 30–31
- ^ Kaufmann & Kaufmann (Neutral States), pp. 94
- ^ Hogg, pp. 118–119
- ^ Kaufmann & Kaufmann (Neutral States), p. 94
- ^ Boyd 2017, pp. 111-112
- ^ DiNardo 2010, p. 130
- ^ Boyd 2017, pp. 87-88
- ^ Boyd 2017, pp. 94-95
- ^ Hogg, p. 121
- ^ Hogg, pp. 121–122
- ^ Kaufmann & Kaufmann (Fortress France), p. 14
- ^ a b Kaufmann, Kaufmann & Lang, p. 208
- ^ Dunstan (Introduction)
- ^ Moorhouse 2019, pp. 159, 194, 255
- ^ Kauffmann (Fortress Europe), pp. 116–117
- ^ Zaloga, p. 70
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