Naisaare Island – one of the most secret sites of the Soviet era

The so-called “American Battery” with 9.2-inch guns is located at the western end of the island, about 200 m from the shore. It was originally intended for 130 mm guns, but was later equipped with guns supplied from the United States. They were operated by electricity, ammunition was delivered by elevators. The command post was combined with a power plant and ammunition storage. In 1918, three positions were blown up, but one remained intact.

Naisaare Island was home to one of the largest Soviet naval mine storage and assembly complexes in the Baltics during the Soviet era. It was built in 1950–1956 to quickly mine the western part of the Gulf of Finland if necessary, and the territory was a closed military zone for civilians. Naval mines were assembled, repaired, stored and transported there via the island's narrow-gauge railway to the port.