Saimaa Canal
On 16 July 1956, the republic was incorporated into the Russian SFSR as the Karelian Autonomous Soviet Socialist Republic. This move can perhaps be explained in the context of the general post-war improvement of Finno-Soviet relations, which also included such steps as the Soviets' return of the Porkkala Naval Base leased territory to full Finnish sovereignty (January 1956), and leasing Maly Vysotsky Island and the Soviet section of the Saimaa Canal (conquered by the USSR in 1940 and 1944) back to Finland (1963).