SFK meaning in Military and Defence ?

The Swedish Volunteer Corps (Swedish: Svenska frivilligkåren) during the Winter War numbered 9,640 officers and men. Sweden was officially non-belligerent during the war, so the Corps was used by Finland. The Swedish volunteers were in the front lines in the northern Salla area starting from February 28, 1940. Their losses included 33 dead, 10 missing, 50 wounded, and 130 disabled by frostbite. There were also 25 aircraft that served in the Swedish Voluntary Air Force, F19. Swedish volunteers also defended Turku in an anti-aircraft battery.

By the end of the war, the Volunteer Corps was composed of 8,260 Swedes, plus 725 Norwegians, and 600 Danes. They demonstrated a strong Nordic unity that was symbolized in their "four brother hands" insignia which represented Finland, Sweden, Norway, and Denmark.