Found the file called Sky_kuurteleska in sky textures.
Battle of Kuuterselkä in 14th - 15th of June 1944 between Soviet Union and Finland.
After the succesful breakthrough at Valkeasaari, the Red Army advances towards the second line of defense, the Vammelsuu-Taipale line. They mount a large spearheaded attack against the Finnish positions and puncture a deep hole at Kuuterselkä.
A strong attack against the Finnish defensive line results in a breakthrough and loss of VT-line. A fierce counterattack by the finns is repelled and the finns are forced to leave VT-line as a whole.