The Finnish garrison era

Though Finland had declared independence in 1917, Viapori was still held by the Russians when the Finnish Civil War broke out in early 1918; in mid-March, they turned part of the fortress over to the Reds fighting in the Civil War. The Whites soon gained the upper hand, though, being reinforced by German troops that landed at Hanko in early April.

The Russian garrison on Viapori remained neutral itself in the Civil War and gradually vacated the fortress. The Whites set up a prison camp for Red prisoners on Viapori, up to 6,000 of them. Some of the prisoners were executed, and others died of disease due to the poor conditions in the fortress. The last prisoners were removed in March 1919.

In May 1918, the fortress was renamed Suomenlinna (‘Fortress of Finland’) to reflect Finland’s independence, and it was taken over by the Finnish government. Soon, the fortress was used to quarter various units of the Defence Forces that could not be accommodated elsewhere. Repairs gradually got under way, and tourists also began to visit the islands.

When the Winter War broke out in 1939, the forces stationed on Suomenlinna included anti-aircraft and artillery units. There was also a submarine base. During the Continuation War (1941–1944), German military personnel were also housed on Suomenlinna.

After the war, only a few military units remained on Suomenlinna; but it was not until the mid-1960s that the Defence Forces announced that it would be vacating the fortress completely. When the Suomenlinna Coastal Artillery Regiment moved out in 1972, Suomenlinna was turned over to civilian administration. Only the Naval Academy remains on Suomenlinna to this day.