The Krepost Sveaborg was an Imperial Russian system of land and coastal fortifications constructed around Helsinki during the First World War. The purpose of the fortress was to provide a secure naval base for the Russian Baltic fleet and to protect Helsinki and block routes to Saint Petersburg from a possible German invasion. Krepost Sveaborg was part of Peter the Great's Naval Fortress, a coastal fortification system protecting access to Saint Petersburg by sea. The central part of Krepost Sveaborg was the old fortress of Suomenlinna where the fortress headquarters were located. Due to technological advances in artillery the old fortress was no longer capable of providing a sufficient protection, and a new main defensive line was built well beyond the old fortress boundaries. New coastal artillery guns built on outlying islands protected Krepost Sveaborg from the sea, while fortified lines constructed around Helsinki were intended to stop any attacks on land. The primary coastal guns were 10 in (254 mm) model 1891 guns and 6 in (152 mm) model 1892 Canet guns. Older 11 in (279 mm) model 1877 guns were also used. In summer 1917 the fortress had two hundred coastal or anti-landing guns, of which 24 were 10-inch guns in six batteries, 16 were 6-inch Canet guns in four batteries and twelve were 11-inch guns in three batteries.^[1]: 31 The artillery used in land fortifications included older coastal guns, old fixed carriage guns and newer light field guns. In March 1917, Krepost Sveaborg had a total of 463 guns, although many of them were obsolescent.^[1]: 25 Krepost Sveaborg was still partly incomplete in 1917 when the February Revolution halted most of the construction work. Some further construction work was carried out during the remaining year, but all work halted during the October Revolution. Following the Finnish Declaration of Independence, parts of the land fortifications were used in the Finnish Civil War. The coastal fortifications were later taken over by Finland to protect Helsinki, while the land fortifications were mostly abandoned and disarmed.^[2][3]

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Krepost Sveaborg
Part of Peter the Great's Naval Fortress
Helsinki, Finland
Overall plan of Krepost Sveaborg
Krepost Sveaborg
Coordinates	60.14°N 24.98°E / 60.14; 24.98
Type	Fortress
Site history
Built	May 1914 (1914-05) — 1917 (1917)
Built by	Russian Empire

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Sweden had ceded Grand Duchy of Finland to Russian Empire as the result of the Finnish War of 1808—1809 and along with it the fortress of Sveaborg, Finnish: Viapori, the present day Suomenlinna. The fortress protected the southern Finland and became a naval base for the Russian Baltic Fleet. After the end of the Napoleonic Wars many new buildings were built to improve the living conditions on the fortress, but the fortifications were neglected. After the start of the Crimean War in 1853 construction of new fortifications began on the other nearby islands and on the southern shore of Helsinki peninsula. In 1854 an Anglo-French naval fleet entered the Baltic Sea, hastening the work. These fortifications protected the flanks of the fortress and provided depth to the defence, but the problem of obsolescent artillery was not solved. Thus, when the fleet attacked the fortress on the 6th of August 1855 they were able to bombard the fortress for two days from a distance of 4–5 km (2.5–3.1 mi) while the best Russian guns had a maximum range of 2,500 m (8,200 ft).^{[1]: 9–11 [4][5]}

After the Crimean War, the fortifications of Viapori were improved by building artillery casemates and new bomb-proof buildings. Vallisaari, just east of Suomenlinna, was the site of the first new construction works. The harsh suppression of the Polish January Uprising of 1863 and the resulting criticism soured the relationships between Russia and western Europe and hastened the fortification works. Between 1863 and 1864 redoubts were built on Vallisaari, Kuninkaansaari and Santahamina islands. In 1860s and 1870s Russia purchased and then built under license new Prussian Krupp rifled breech loading guns which were also used in Viapori. A total of 32 new bomb-proof stone powder cellars were built by the beginning of the 1870s, further improving the defences. The Russo-Turkish War of 1877–1878 was the next crisis that threatened the peace between Russia and England, with new batteries being built at Viapori on Kuninkaansaari and older ones improved or rebuilt. New technology in the form of telegraph, railway lines and searchlights began to be used. Improvements in artillery and ammunition forced improving the gun positions by covering the old walls and fortifications with a thick earthen walls. With high-explosive shells appearing at the end of the 19th century earth and stone were no longer sufficient and first concrete fortifications with steel doors were built in Viapori. Continually improving guns resulted increased range, necessitating rangefinders, while heavier guns and ammunition required improving piers, roads, cranes and ammunition carts to transport the guns or move ammunition from magazines to guns. Despite the improvements the funds and resources allocated to the fortress were not sufficient to keep pace with the evolution of military technology. While parts of the fortress or were improved and new weapons or equipment were received, the overall condition of the fortress became ever more obsolescent, and the vulnerability of the flanks and rear were a lasting problem. By the end of 1880s and early 1890s Viapori could no longer be considered a proper fortress but only a coastal position, capable of defending only against an enemy coming directly from the sea. The primary role of the fortress became more one of internal politics, as it helped the Russians maintain control of Helsinki.^{[1]: 12–15 [5][6]}

In the 1890s the priority of the fortification works in the Baltic Sea had been the protection of the ice-free port of Liepāja, and the Kronstadt fortress protecting Saint Petersburg, relegating Viapori to a secondary status. After the losses during the Russo-Japanese War and in light of the rising might of the Imperial German Navy, Liepāja was considered too vulnerable for a main fleet base, and the decision to build Peter the Great's Naval Fortress was made. In the new plans the main line of defence against the enemy was at the Porkkala-Tallinn line with Tallinn also the new main base for the Russian Baltic Fleet. Helsinki was to be a base for torpedo boat flotillas. The construction of the Tallinn naval base was delayed however, and with the new ships being constructed to replace the losses suffered against Japan the Russian Navy was forced to rely more on Helsinki despite the obsolete armament and inadequate fortifications at Viapori. As the threat of war in Europe grew, it became essential to expand the fortress to provide a necessary protection for the naval base. Until 1910, when the first 152 mm Canet guns arrived, the only modern weapons at Viapori were 57 mm quick fire guns with the rest of the artillery designs dating from the Russo-Turkish War. The first new 254 mm guns arrived in 1913, but it was not until early 1914 that construction of the first new batteries began on Melkki and Isosaari. During the First World War the new Krepost Sveaborg was built to substantially expand the old fortress. A new main line of defence was constructed on the outlying islands, pushing the defensive line several kilometers southward, thus providing a secure outer anchorage south of the old fortress for larger warships without the need to navigate the narrow straits leading to the inner anchorage at Kruunuvuorenselkä. The older parts of the fortress became a second line of defence and the main storage areas. The rear of the fortress was finally protected by land fortifications, at first field fortifications on the Helsinki peninsula built in 1914, and, later, an outer line of fixed fortifications.^{[1]: 15–17 [3][7][8]}

At the start of the First World War Krepost Sveaborg was subordinated to the Russian 6th Army. In summer 1916 Krepost Sveaborg was subordinated to Baltic Fleet. At the start of the war Krepost Sveaborg was divided into three defensive areas, with the sea front forming one defensive area and the land front divided to Pasila and Laajasalo-Herttoniemi areas. The sea front was further divided into six sectors, with sectors 1–4 at the old fortress, sector 5 at Melkki and sector 6 at Isosaari. The sea front was divided into main line of defence from Melkki to Isosaari and second line of defence from Lauttasaari to Santahamina at the end of 1914. As the new batteries were constructed Melkki was relegated to second line of defence and Lauttasaari to land front in spring 1915. At the land front new defensive lines were constructed from 1915 onward further away from the city center. The new land front was divided into three sectors: eastern, northern and western.^[9] Krepost Sveaborg was also responsible for a larger fortification district that included coast line west of the fortress until Hanko.^{[1]: 23–24}

At the start of the war the fortification artillery units manning the fortress were organized into nine artillery companies and a machine gun detachment. In April 1915 the fortification artillery units were reorganized into a single fortification artillery regiment with three battalions and a machine gun company. Four companies manned the coastal forts at sea front. In June 1916 the regiment was divided in two, with 1st regiment responsible for the seaward defence and the 2nd for the landward defence. Both regiments had ten companies in three battalions. The 1st regiment was divided into three defence detachments, with south-western and south-eastern detachments responsible for the main line of defence on the outlying islands with the newest guns, while the third detachment manned the second line on the old fortress. The artillery regiments had a common supply unit responsible for the weapons, ammunition, transportation between islands etc. A signals company built and maintained the communication lines. The minefields around the fortress were built by the Krepost Sveaborg mine company, from 1915 a mine battalion. In 1916 the fortress was reinforced by the mine battalion from Vladivostok fortress. Construction and engineering department of the fortress headquarters organized the construction works of the fortress with engineering and sapper units as well as the civilian workers.^{[1]: 24–25}

Infantry units at the fortress manned the landward defences and provided detachments on the coastal forts for anti-landing and close defence duties. The peacetime Krepost Sveaborg fortress infantry regiment was reinforced by conscript units, which in 1915 were organized as the 427th and 428th infantry regiments to a new 107th infantry division which was sent to front line after a training period. In spring 1916 regiments from the new 116th division manned the fortress. At the autumn of 1916 units from different fortresses were brought to Krepost Sveaborg and organized into the 128th infantry division. In July 1917 the fortress was manned by the fortress infantry regiment and the 428th Lodeynoye Pole infantry regiment of the 128th division. In October 1917 the 128th was replaced by the 29th infantry division, badly mauled at the front and brought to Krepost Sveaborg for rest. At January–February 1918, when Finland gained its independence, Krepost Sveaborg had six infantry regiments: the 696th revolutionary regiment, the fortress infantry regiment and 113th, 114th, 115th and 116th regiments of the 29th infantry division.^{[1]: 24–26}

Construction workers included Russian soldiers but also Finnish civilian workers and forced labour using prisoners transported from far east. Finns were exempt from conscription, and thus there was available manpower for fortification works. The payment for fortification works was slightly above average for manual labour, and made it an attractive option particularly for many rural workers. In 1915 when large scale construction of fortifications around Finland began Russians instituted a work responsibility for Finns based on wartime emergency law to obtain the necessary labour force. To ease the manpower shortage Russians brought convicted prisoners from far east to Finland in summer 1916 as forced labour. Approximately 2000-3000 men, including Chinese, Kyrgyz and Tatars, were employed as lumberjacks around Espoo and Sipoo. Kyrgyz were mainly guards. Asian workers were transported back to Russia already in 1917 however, citing the workers to be unaccustomed to the northern climate and possible threat of rebellion. The total number of workers in not known, but an estimated 10 000 to 15 000 men were used in construction works around Helsinki and up to 100 000 total in Finland. Complicated bureaucracy delayed the construction works, and the supervision of the works was also poor, leading to a widespread graft.^[10][11]

To protect Krepost Sveaborg and the naval base in particular from a German attack from land the fortifications were built to protect the fortress. The first fortifications were hastily built in 1914 to block access to the Helsinki peninsula and to guard the eastern flank of Laajasalo and Santahamina by a scarce line of fortifications at Ruskeasuo-Pasila-Käpylä-Koskela-Viikki-Herttoniemi-Roihuvuori. Lauttasaari, Meilahti and Laajasalo were also fortified to some extent. It was also planned to fortify Kulosaari and Vartiosaari. These first fortifications were field fortifications located 6–7 km (3.7–4.3 mi) from the city center, with the defence concentrated at fortified hilltop redoubts.^[3][9]

In early 1915 it was decided to build new defenses further away from the city center. The new defenses were stronger fixed fortifications with positions quarried into rock or dug into ground. Fortifications were built from wood and stone masonry as well as concrete. New fortifications had a network of defensive structures, with trenches, rifle pits, machine gun nests, barbed wire obstacles, shelters and roads. Artillery batteries were located 0.5–1.5 km (0.31–0.93 mi) behind the front line, often located on reverse slope. Artillery batteries had 2–6, typically four, guns. Heavily fortified caponiers providing flanking fire were built on places of the front line. First a northern line was built at Leppävaara-Kaarela-Pakila-Pukinmäki-Myllypuro-Vartiokylä. Construction on a western line from Leppävaara to Westend via Tapiola began shortly afterwards. In late 1915 it was decided to build an outer line of defence on the northern and eastern sectors, extending the fortifications northward and in the east from Pukinmäki to Malmi, Mellunkylä and Vuosaari. Fortification works continued until the February revolution of 1917, and some work was done until early 1918. The land front was divided into three sectors, eastern, northern and western with 36 bases, numbered I-XXXVII. The bases were usually centered on hilltops with the strongest defences.^{[3][9][14][15]}

The basic front line fortifications were open or covered machine gun nests, rifle pits, observation posts and shelters. Most of the structures were designed to be covered with a concrete roof poured on wooden planks occasionally reinforced with railway tracks. Some of the positions were built with stone or logs. Many of the fortifications have been left uncovered however, built only to a point where adding the missing roof could be accomplished quickly. The basic fortified types are a type A square machine gun nest,^[16] type B square rifle or machine gun pit, type C rounded rifle or observation pit,^[17] type D oval rifle pit with several firing ports^[18] and types E and F large rifle positions for multiple shooters.^[19] There is considerable variation between individual structures among the basic types, with newer positions generally built larger and stronger.^[15][20][21]

Coastal fortifications on the naval front protected Krepost Sveaborg from an attack from the sea. During the war new fortifications were built on the outlying islands pushing the defences outward to protect the ships in the harbour from new modern guns. During the First World War the naval front of the fortress was modernized almost completely. The new gun batteries can be divided into four types: heavy long range batteries, close range batteries, anti-landing batteries equipped with field guns and anti-aircraft batteries which appeared during the war for the first time. The naval front was divided into six sectors at the start of the war with sectors 1-4 comprising the old fortress, sector 5 Isosaari and sector 6 Melkki. The central fire control post was located in Vallisaari. As the new coastal forts were completed the organization changed and the naval front was divided into two parts: an outer main line of defence from Melkki to Isosaari and an inner second line of defence from Lauttasaari to Santahamina. The naval front command post was located in Vallisaari and the main artillery command post in Kuivasaari.^{[1]: 23–24}

The long range batteries of 10 in (254 mm) and 6 in (152 mm) guns included ten batteries with six 10 inch batteries and four 6 inch batteries, with one more under construction. The basic shape of the batteries is four guns in a row protected from the front by a concrete parapet of approximately 5 m (16 ft) thick with traversal walls between the gun positions. The batteries had no rear protection. Shelter for crew and ammunition cellars were built into and under the front parapet and the traversal walls. While the basic plan is similar, each battery is unique depending on the terrain. For the 10 inch guns the average distance between guns is 40 m (131 ft), but on smaller island such as Katajaluoto the guns are only 30 m (98 ft) apart while the larger Isosaari battery (No 1) has guns 50 m (164 ft) apart. Similarly the 6 inch batteries have guns 35 m (115 ft) apart on average, but in the very cramped Harmaja battery the distance between guns is only 20 m (66 ft) and the battery is not built on straight line but in a crooked L-shape. Many batteries have an icon closet framed with granite.^{[1]: 27–28}

Krepost Sveaborg never did see action against Germany in Russian hands. After the Russian revolution the treaty of Brest-Litovsk ended Russia's participation in the First World War. The treaty affirmed the independence of Finland and required Russian troops to leave from the country. Of the approximately 35 000 Russian soldiers and sailors who were around Helsinki in January 1918 most were demobilized and sent home or simply left by 15 March. Around one thousand joined the Finnish Red Guards in the Finnish Civil War. The Soviet leadership ordered Krepost Sveaborg headquarters to begin preparations to abandon the fortress and destroy what could not be evacuated in case it would fall into German hands. Some field guns were transported to Russia, but all the coastal guns were left. On 3 April 1918 German Baltic Sea Division landed in Hanko, after being requested by the White Senate of Vaasa to participate in the Finnish Civil War against the Reds. Russian Baltic fleet officers had made an agreement with the Germans allowing a safe departure for the warships and disarming the fortress. Most of the Russian ships left by mid-April, but the last ships left only in May–June 1918. The disarmament - removing locks from the guns, cutting the cables controlling the mines and destroying the mine control stations - had to be done in secret as an agreement between Soviet government and Finnish Red Guards had promised the latter all the fortifications. When the Germans arrived in Helsinki the Red Guard could only use some of the land front fortifications in Leppävaara and Ruskeasuo, and the Germans with a well equipped and trained numerically superior force quickly captured Helsinki between 11th and 13 April. The Russian guards ceded the coastal forts to Germans according to their agreement. The disarmament of Krepost Sveaborg, denying the Reds from using it, was used in White propaganda by how Allan Staffans had duped the Russians and removed the locks without authorization; but actually the disarmament occurred with the order of the fortress commander and with the knowledge of naval headquarters.^[24] On 12 May Krepost Sveaborg was renamed Suomenlinna to celebrate the new independency.^{[1]: 20–21 [3][25][26]}

After First World War the fortifications of Krepost Sveaborg were taken over by Finland. Most of the land front fortifications were disarmed, stripped of useful equipment and abandoned. Much of the land front fortifications with steel reinforcements were destroyed in the inter war period and the steel sold as scrap. During the Second World War an inventory of the land front fortifications was conducted regarding their usefulness, with the larger shelters quarried into the rock under particular interest as facilities for war industry, emergency hospitals or storage. Some of the land front shelters are still used as storage space. As settlement spread during the urbanization after the Second World War many of the fortifications were destroyed as new suburbs were constructed. The coastal fortifications were used by the Finnish coastal artillery to protect Helsinki. Most of the islands remained in military use and were thus spared from vandalism. All structures of the Krepost Sveaborg fortifications around Helsinki, both land and sea fronts, were declared protected historical sites by the Finnish National Board of Antiquities in 1971.^[27][28]