Following the Nazi invasion of the Soviet Union in June 1941, the Nazis encouraged Ukrainians, who were former soldiers of the Red Army and who had been captured, to join their cause. Tens of thousands of Ukrainians volunteered for service in the German security services, as well as Lithuanians, Latvians, Estonians and others. Those former Ukrainian Soviet Army prisoners and local Ukrainians from Polish West Ukraine (who volunteered for service in Aktion Reinhard) were sent to the SS training camp at Trawniki. In October 1941 SS-Sturmbannführer Karl Streibel became appointed commander of the camp. Even Himmler visited Trawniki; a number of photographs exist, recording his visit. These volunteer units were called "Trawnikis" or "Askaris" by the local population. The Germans called them Hilfswillige or Hiwis for short, and the volunteers themselves Wachmänner. In Trawniki the Wachmänner received abbreviated military training and exercises, including training for the deportation of Jews. Approximately 2,000 - 3,000 guardsmen passed through the training camp during the two and a half years of its activity. Some of them were organised into two battalions with four companies each, about 1,000 men altogether. The size of a company was 100 - 200 men. One was a training company for squad commanders (Zugführer). One or two companies were stationed permanently in Lublin for security duties. Other Trawniki units carried out guard duties in various institutions and labour camps in the Lublin district.