Editing Mannerheim Line (section)

==History of construction==
===Background===
[[File:Mannerheim3.jpg|thumb| [[Carl Gustaf Emil Mannerheim]] in 1937]]

After the [[October Revolution]] in the [[Russian Empire]], the Finns [[Finland's Declaration of Independence|declared independence]] in 1917. Although the [[Russian Soviet Federative Socialist Republic|Soviet Union]] recognized Finland's independence, the Finns did not trust their sincerity. The relationship between the two countries deteriorated, with Soviet Russia supporting the [[Red Guards (Finland)|Red Guard]] during the [[Finnish Civil War]] in 1918. After the victory of the [[White Guard (Finland)|White Guard]], a group of Finnish communists fled to Soviet Russia and established the [[Communist Party of Finland]].<ref name="UittoGeust1">[[#UittoGeust2006|Geust & Uitto 2006]], page 9</ref>

The situation was considered dangerous for a new nation like Finland, especially as the capital of the new communist revolution was nearby [[Petrograd]], (now [[Saint Petersburg]]). Furthermore, before the [[Treaty of Tartu (Russian–Finnish)|Treaty of Tartu]] in 1920, the border area was restless. The former general of Imperial Russia, C.G.E. Mannerheim, strongly opposed the [[Bolshevik]]s (Communists). Construction work on the Karelian Isthmus had already begun when the Bolsheviks won the Russian Civil War in 1922.<ref name="UittoGeust1" /> The line was constructed in two phases: In 1920–1924 and 1932–1939.

===Planning in 1918===
During the civil war of 1918, the Finnish government and high command started to develop defence plans to protect against possible attacks from the Soviet Union. The main such route was the [[Karelian Isthmus]]. The most endangered part of that isthmus was to the west, near the Gulf of Finland, the eastern part was better protected by the natural water-ways of [[Vuoksi]], [[Lake Sukhodolskoye|Suvanto]] and [[Taipaleenjoki]]. The first plans for a defensive line were commissioned by Mannerheim from the Swedish volunteer Lieutenant Colonel A. Rappe at the beginning of May 1918. Rappe's line was placed close to the border and designed to protect two rail lines that crossed the border, which could be used in a counterattack toward Petrograd. When Mannerheim resigned at the end of May, Rappe's plans were abandoned.<ref name="Kronlund1">[[#Kronlund1988|Kronlund 1988]], page 187</ref>

The young nation possessed no guard troops, and the border area was insecure. Security of the border on the isthmus was the responsibility of the 2nd Division and local White Guard units in June 1918.<ref name="Kronlund2">[[#Kronlund1988|Kronlund 1988]], page 127</ref> In that form they were also entrusted with the security of the fortification construction. First efforts were weak depots without any concrete.<ref name="UittoGeust2">[[#UittoGeust2006|Geust & Uitto 2006]], pages 9–14</ref>

The Germans had ordered Colonel [[Otto von Brandenstein]] to investigate defensive positions on the Karelian Isthmus; he delivered his plan on 16 July. He was the first to suggest using the lake isthmuses, where smaller lakes like Lake Kuolemajärvi, Lake Muolaa, Lake Suvanto and the Taipaleenjoki river divided the Karelian Isthmus to the shorter land sections, as defensive positions, his plan was initially approved by the Finnish high command in August 1918. In October 1918, the Finnish government allocated 300,000 marks for the work, which was to be carried out by German and Finnish sappers as well as Russian prisoners of war. However, the money allocated was insufficient and a lack of building materials and a qualified workforce hampered the building of proper fortifications. With Germany's defeat in [[World War I|The Great War]], von Brandenstein's plan was scrapped.<ref name="Kronlund3">[[#Kronlund1988|Kronlund 1988]], page 189</ref>

===Unreinforced concrete bunkers in 1919–1924===
During October 1919 Finnish Chief of Staff Major General [[Oscar Enckell]] sited the line, mostly following the original course that von Brandenstein had presented.<ref name="Kronlund5">[[#Kronlund1988|Kronlund 1988]], page 200</ref> Major J. Gros-Coissy, a member of the French military commission, designed the fortifications together with Finnish Lt Col [[Johan Fabritius]].<ref name="Kronlund4">[[#Kronlund1988|Kronlund 1988]], pages 206, 246</ref> During the first building period, Fabritius suggested moving the defensive line further to the south-east. The general staff discussed the issue, but Enckell's earlier plans were followed. Furthermore, insufficient funds resulted in a disagreement between the officers and Enckell resigned in 1924. Construction work was interrupted for a long period.<ref name="UittoGeust2" />

The prime contractor of the fortifications was the Finnish construction company [[Ab Granit Oy]]. The first hundred small [[bunker]]s were built in 1920–1924.<ref name="UittoGeust2" /> For reasons of cost, the first phase hard fortifications were of unreinforced concrete, which provided only partial protection. The compression density of the concrete was too low to offer resistance to anything larger than medium [[artillery]].<ref name="Edwards13">[[#Edwards2006|Edwards 2006]], pp. 111–112</ref>

===First large bunkers 1932–1937===
[[File:Sk 10 inside beds Winter War.png|thumb|Troop beds in a destroyed bunker on the Mannerheim Line. The bunker is probably Sk 10, built in 1937.]]

The second construction phase started on 1 April 1934, with Fabritius in command of the construction work. He designed two new kinds of bunker, Ink 1 and Ink 2. The bunkers were mainly designed for troop accommodation, but loopholes were crafted into armour plate in 1938 and 1939. A bunker was typically 15–20 meters in length and 5–6 meters wide. A pioneer battalion constructed six bunkers in the [[Inkilä]] sector.<ref name="UittoGeust2" />

Between 1932 and 1938 the defence budget was such that the Finns could only construct two or three bunkers per year. In 1936 and 1937 they constructed two large strong-points, Sk 10 and Sj 4 in the [[Summankylä]] and [[Summajärvi]] areas. Two smaller bunkers, Le 6 and 7, in the [[Leipäsuo]] sector, and Ink 6, in the Inkilä sector, were also built. New bunkers differed from earlier designs in that their troop accommodation was located between the gun chambers, thus saving the cost of expensive [[reinforced concrete]]; the roof was protected by two to three meters of soil and one to three meters of stone rubble.<ref name="UittoGeust5">[[#UittoGeust2006|Geust & Uitto 2006]], page 39</ref>

===The 1938 and 1939 period===
The Karelian defensive fortifications received considerably more funds and resources from May 1938, as the European situation worsened. The Finns built new strongholds and modernized old ones. In Summakylä and Summajärvi they built two large Sk 11 bunkers, a "Peltola", a Sj 5, a "Miljoonalinnake", and an incomplete third Sk 17. These bunkers had better fire shelters, [[ventilation (architecture)|ventilation]] and an observation [[Armoured cloche|cloche]].<ref name="UittoGeust6">[[#UittoGeust2006|Geust & Uitto 2006]], pages 42–43</ref>

In [[Suurniemi]] near [[Muolaanjärvi]], the Finns started the construction of seven new bunkers, Su 1–7. Two others, Su 3 and Su 4, were for accommodation, and the rest were for [[machine guns]] nests. They also modernised those structures built in the 1920s. The older bunkers were given added flank-fire capability and enlarged. Some bunkers' loopholes were simply closed-up as part of a plan to make them more suitable for accommodation or command posts.<ref name="UittoGeust7">[[#UittoGeust2006|Geust & Uitto 2006]], page 44</ref>

The line was still incomplete in November 1939.<ref name="Edwards13" />