The 'Summer War' (in Estonian the 'Suvesõda') was the German and Estonian resistance occupation of Estonia (3 July/21 October 1941).

This little campaign was fought between the Forest Brothers (Metsavennad), the Omakaitse (Estonian militia) and Generaloberst Georg von Küchler’s 18^th Army of Generalfeldmarschsall Wilhelm Ritter von Leeb’s Heeresgruppe 'Nord' against the forces of General Leytenant Konstantin P. Piadyshev’s (from 11 July General Leytenant Aleksandr A. Tyurin’s) Soviet 8^th Army and the internal security forces of the NKVD.

On 17 June 1940, the USSR had occupied Estonia and on 6 August declared the previously independent state to be the Estonian Soviet Socialist Republic. Estonian civilians and potential Soviet opponents were repressed and sent to prison camps and settlements in the USSR during the deportation in June.

When Germany launched its 'Barbarossa' attack on the USSR on 22 June 1941, some Estonians hoped that the Germans would liberate the three Baltic states from Soviet rule. Heeresgruppe 'Nord' had Leningrad, at the eastern end of the Gulf of Finland, at its objective and as it advanced to the north-east entered Estonia. In northern Estonia, the Soviet 'destruction battalions' (paramilitary units under the control of NKVD in the western USSR to perform internal security tasks) offered a fierce defence of the area, and it was the last area to be occupied by the Germans. Around 12,000 Estonian partisans of the Forest Brothers grouping attacked the NKVD forces and the 8^th Army. After the 18^th Army had crossed Estonia’s southern border on 7/9 July, the Forest Brothers organised larger units, and engaged elements of the 8^th Army and destruction battalions at Antsla on 5 July 1941.

In the Battle of Kautla the Forest Brothers engaged destruction battalions during July 1941 in an undertaking which included a series of murders of civilians by the destruction battalions. On 24 July, an extermination battalion murdered two adults and set their farm on fire. In the coming days, the extermination battalion undertook the systematic murder of all civilians in the region and burning of their farms. The Kautla farm was burned down by the Soviet force with the family and staff of six persons still inside. In total, more than 20 civilians were murdered, many of them after they had been tortures, and more than 10 farms destroyed. The low toll of human deaths in comparison with the number of burned farms resulted from the fact that Henn-Ants Kurg’s Erna long-range reconnaissance group of Estonians in Finnish service broke the Soviet blockade of the area, allowing many civilians to escape.

On 6 July there was a larger engagement in Vastseliina, where the Forest Brothers prevented Soviet destruction of the town and trapped the extermination battalion leaders and local communist administrators. On the following day, 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 behind the Pärnu river and Emajõgi river line, and secured southern Estonia by 10 July. The NKVD murdered 193 people in Tartu prison as they retreated on 8 July.

The 18^th Army resumed its advance through Estonia in collaboration with the Forest Brothers, and a joint Estonian and German force took Narva on 17 August.

By the end of August, Tallinn had been surrounded even as the majority of Vice Admiral Vladimir F. Tributs’s Baltic Fleet was still in the city’s harbour. On 19 August the final German assault on Tallinn began, and the combined Estonian and German force took the city on 28 August even as the 'Evacuation of Tallinn Operation' was effected with significant Soviet losses. After the Soviet forces had been driven out of Estonia, however, the Germans disarmed the Forest Brother groups, and replaced the Estonian flag flying over Tallinn was with the German flag.

On 8 September, German and Estonian units launched 'Beowulf' to clear Soviet forces from the West Estonian archipelago. After launching a series of diversionary attacks to confuse and distract the Soviet defenders, they had taken the islands by 21 September.

Alongside the overt fighting between the partisan groups and the Soviet forces, and the reintroduction of a scorched earth policy, the NKVD committed acts of terror against the civilian population, many buildings being burned, because their occupants were regarded as co-conspirators. Thousands of other civilians were killed, while many towns, schools, services and other buildings were torched. In August 1941, the whole population of Viru-Kabala was killed. The destruction battalions also on occasion burned people alive, and in overall terms the destruction battalions killed 1,850 unarmed civilians or partisans.

During the fires of 12/13 July, the headquarters of the Estonian Defence League, the campus of the faculty of veterinary medicine and agriculture of the University of Tartu, and other university buildings were burned. Several of the university’s libraries and 135 major private libraries were destroyed, the losses including 465,000 books, many archive materials and 2,500 pieces of art.

Some 3,237 farms were destroyed, while 13,500 buildings were destroyed. Compared with those of 1939, by 1942 the decline in animal populations were severe: horses down by 14%, dairy cattle down by 34%, pigs down by 50%, sheep down by 46% and fowl down by 27.5%. Much in the way of supplies was looted for use in the USSR.

After the 'Summer War', the German forces entered the USSR via the Baltic states and conscripted Estonians to be part of the 20^th Waffen-Grenadierdivision der SS (estnische Nr 1), the 15^th Waffen-Grenadierdivision der SS (lettische Nr 1) and the 19^th Waffen-Grenadierdivision der SS (lettische Nr 2), although the majority of the men in the latter two formations were Latvians.