Prior to World War II, Estonia, Latvia, and Lithuania were important centers of espionage conducted against the Soviet Union and the British Secret Intelligence Service maintained stations at Stockholm, Sweden, and Helsinki, Finland, to supervise operations conducted from Tallinn, Riga, and Vilnius, usually with the cooperation of the local intelligence apparatus. Following the Soviet occupation of all three countries in 1945, the SIS attempted to infiltrate émigrés across the Baltic from Hamburg via a base on Bornholm Island, Denmark, but the scheme failed because of hostile penetration by the Soviets.