Säkkijärven polkka ("the Säkkijärvi polka") is a well-known folk tune from Finland, popular with Finnish accordionists to the extent that it can be called their national anthem. It was especially popularized by Viljo "Vili" Vesterinen (1907–1961). The tune was first recorded in Säkkijärvi (now Kondratyevo in the Leningrad Oblast, Russia), and the words sometimes sung to the tune point out that Säkkijärvi itself might have been lost, but that Finns could at least keep the polka.
During the Continuation War, the Finnish Army discovered that the retreating Soviets had scattered radio-controlled mines throughout the re-captured city of Viipuri. These mines were set off when a three-note chord was played on the frequency the radio was tuned to, causing three tuning forks (of which each mine had a unique combination) to vibrate at once. Once the Army and Yleisradio experts discovered how the mines worked, a Yleisradio mobile transmitter was brought to Viipuri, and Vesterinen's polka was played on the same frequencies the mines used. They played the song continuously from August 1941 until 2 February 1942, about 1,500 times. It had been calculated that it would take at least three months for the batteries of the mines to be empty.
Säkkijärven polkka is also the title of the eponymous film directed by Viljo Salminen (1908–1992) in 1955.