The Summer War (Estonian: Suvesõda) was the occupation of Estonia during the Second World War. It was fought between the Forest Brothers (Metsavennad), the Omakaitse, and the Wehrmacht's 18th Army against the forces of the 8th Army of the USSR and the NKVD. Background On June 17, 1940, the USSR occupied Estonia and on August 6, Estonia became a Soviet Socialist Republic. Estonian civilians and potential Soviet opponents were repressed and sent to prison camps and settlements in the Soviet Union during the deportation in June. Invasion When the Third Reich invaded the Soviet Union on June 22, 1941, some Estonians hoped that the Germans would liberate the Baltics from Soviet rule. The Army Group Nord, led by Marshal General Wilhelm Ritter von Leeb, invaded Estonia. In Northern Estonia, the Soviets' Destruction battalions fiercely defended the area, and it was the last to be occupied by Germany, Around 12,000 partisans of the Estonian Forest Brothers attacked the NKVD forces and the 8th Army. After the German 18th Army crossed the Estonian southern border on July 7–9; the Forest Brothers organized bigger units. They took on the 8th Army units and destruction battalions at Antsla on 5 July 1941. Kautla Massacre In the Kautla Massacre, twenty civilians were murdered and many were tortured before they were killed. The proportion of destroyed properties to murdered civilians was because the Finnish volunteer group commanded by Henn-Ants Kurg named the ‘Erna long-range reconnaissance' broke the Red Army's blockade and evacuated civilians. Liberation of territory On July 6, 1941, 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 the Forest Brothers reorganised into the Omakaitse militia. The battle of Tartu lasted for two weeks and destroyed a large part of the city. Under the leadership of Friedrich Kurg, the Forest Brothers drove the Soviets out, behind the Pärnu River – Emajõgi River line and secured southern Estonia by July 10.[need quotation to verify] The NKVD murdered 193 people in a Tartu Prison on their retreat on July 8 The 18th Army resumed their advance in Estonia by collaborating with the Forest Brothers. The joint Estonian-German forces took Narva on 17 August. Capture of Tallinn By the end of