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.

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 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.

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.

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.

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.

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 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.

The guns for this battery arrived, bringing the total sea front number to twenty, but the construction was not completed before the war ended.

The measurement pavilions had simple wooden walls and sheet metal roof protecting them from the elements and were 4–6 m2 (43–65 sq ft) in size.

New fortifications had a network of defensive structures, with trenches, rifle pits, machine gun nests, barbed wire obstacles, shelters and roads.

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.

[3][9][14][15] The basic front line fortifications were open or covered machine gun nests, rifle pits, observation posts and shelters.

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.

At the end of the war, it comprised (from west to east): Miessaari and Pyöräsaari, Rysäkari, katajaluoto, Harmaja, Kuivasaari, Isosaari, Santahamina and Itä-Villinki islands and Skatanniemi cape.

Construction of bakeries on the outer forts began after the February revolution as a result of the demand of an artillery regiment committee formed by the soldiers.

The islands also formed the seam between naval and land fronts, and Miessaari had also a land-facing battery number 115 of six 6 in (152 mm) 190 pood model 1877 siege guns, supporting the base XXXIV in Haukilahti-Westend area.

The guns, transported from Vladivostok, were installed by January 1915 and the entire battery with ammunition cellars and concrete command tower was finished in spring 1916.

The island's central location and size made it the most heavily armed coastal fort and it was part of the plans for expanding Krepost Sveaborg already in 1909.

The primary combat objective of the batteries on the second line was to prevent enemy ships from passing through Kustaanmiekansalmi or Särkänsalmi straits to the inner anchorage on Kruunuvuorenselkä.

The second line included Lauttasaari, Melkki, Pihlajasaaret, Harakka, the central citadel at Suomenlinna, Lonna, Vallisaari, Kuninkaansaari, Nuottasaari and Vasikkasaari.

The guns were on temporary wooden platforms, and the battery was relocated already in August as construction of new fortified concrete anti-aircraft positions and shelters began.

[1]: 92–96 Lonna 60°9′16.17″N 24°59′23.2″E / 60.1544917°N 24.989778°E / 60.1544917; 24.989778 is a small island north of Iso Mustasaari that was used as the main naval mine depot of Krepost Sveaborg.

Eight storage magazines housed weapons, ammunition, mines and torpedoes with a narrow gauge railway built on the island connecting them to the main pier.

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.

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.

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.

A coastal artillery museum has been built on Kuivasaari and the island is no longer in active military use, but still officially restricted area.