Treasure Island under Construction, circa 1937 Treasure Island, site of the 1939 International Exposition, was built with dredged soil from the Bay. The island was to become San Francisco International Airport in 1941. However, the Navy seized the island in 1942, after World War II began, and it became Treasure Island Naval Station. Situated between the world's two largest bridges spanning San Francisco Bay, Treasure Island was the site of the 1939 International Exposition. Built of bay dredged dirt, the island was to become San Francisco International Airport in 1941. However, the Navy seized the island in 1942, shortly after World War II began, and it became Treasure Island Naval Station.