After the German 18th Army crossed the Estonian southern border on July 7–9, the Forest Brothers organized themselves into bigger units. They took on the 8th Army units and destruction battalions at Antsla on 5 July 1941. The next day, a larger offensive happened in Vastseliina where the Forest Brothers prevented Soviet destruction of the town and trapped the extermination battalion chiefs and local communist administrators. On July 7, the Forest Brothers were able to hoist the Estonian flag in Vasteliina. Võru was subsequently liberated and by the time the 18th army arrived, the blue-black-white flags were already at full mast and the Forest Brothers had organised into the Omakaitse militia.