Porkkalanniemi (Porkala udd) is a peninsula in the Gulf of Finland, located at Kirkkonummi (Kyrkslätt) in Southern Finland.
The peninsula had great strategic value, as coastal artillery based there would be able to shoot more than halfway across the Gulf of Finland. If the same power controlled the Estonian coast, on the opposite side of the gulf, it would then be able to block Saint Petersburg's naval access to the Baltic Sea. The distance to Estonia at the closest point is only . Porkkala is furthermore located only from Helsinki, the Finnish capital, and a foreign power based there would be able to exert significant pressure on the Finnish government.
Nowadays, the coasts of the peninsula are popular birdwatching areas during the spring migrations of Arctic geese and other waterfowl.
At the end of the Second World War, the Soviet Union secured the rights of lease to a naval base at Porkkala, in accordance with the Moscow armistice agreement that ended the Continuation War between Finland and the Soviets on 19 September 1944.
Porkkala thus replaced the peninsula of Hanko, which had been leased to the Soviets as a naval base in 1940–41. A large area centered on the peninsula, including land from the municipalities of Kirkkonummi, Siuntio and Ingå and almost the entire area of Degerby, was leased to the USSR from 29 September 1944, ten days after the armistice. At the time of the Soviet take-over of the area, there were about 7200 Finnish inhabitants and all were evacuated during ten days in September 1944.
Beyond its military use, the naval base served to apply political pressure on the Finnish governments and also to help build a Soviet espionage network.
It was immediately placed under a military commander, Neon Antonov (1907–1948), who remained in office until June 1945, when he was transferred to command the Amur River flotilla, in preparation for the war against Japan.
According to the armistice of 1944, the area was leased to the Soviet Union for 50 years.