The island served as a base for pilots at the turn of the 19th century. They lived in a brand-new residential building, where army staff and their families later settled. The building still welcomes visitors arriving at the north shore.
From 1946 to summer 1965, a military central weather station operated on the island. During the Second World War, a German-made Freya air surveillance radar – renamed Raija in Finland – was placed on the island.
Military staff and their families formed a tight residential community on Vallisaari. The population was at its largest in the 1950s, with 300 people. The residents had their own shop and school. People played sports, cultivated small pieces of land, and ran an amateur theatre company, and children played on the island’s rocks and in the forests. People gathered around the island’s first television set to watch exciting TV shows in the same way as they gathered on the high points of the island to watch the Sputnik satellite fly over Helsinki. The island’s history also has its dark side: in July 1937, a destructive explosion happened on the island, and 12 people died.