Estonian military units within the Red Army began to be formed in January 1942, from among ethnic Estonians living in the USSR. A Soviet source suggests that in May 1942 there were nearly 20,000 Estonians in the national units. The 8th Estonian Rifle Corps, as these units came to be called after September 1942, reached the front in Velikie Luki in December 1942 and suffered heavy losses in battle as well as the defection of about 1,000 men to the German side. After Velikie Luki the Rifle Corps was replaced with other nationalities from the USSR. The corps' major activity in the latter part of the war was participation in the battles for Estonia.