The construction of the Ebensee subcamp began late in 1943, and the first prisoners arrived on November 18, 1943, from the main camp of Mauthausen and its subcamps. The main purpose of Ebensee was to provide slave labor for the construction of enormous underground tunnels in which armament works were to be housed, safe from bombing. These tunnels were planned for the evacuated Peenemünde V-2 rocket development but, on July 6, 1944, Hitler ordered the complex converted to a tank-gear factory. One tunnel was used as a petroleum refinery. The SS used several codenames: Kalk (English: limestone), Kalksteinbergwerk (English: limestone mine), Solvay and Zement (English: cement) to conceal the true nature of the camp.
27,278 male inmates were sent to Ebensee. Between 8,500 and 11,000 died in the camp. Jews formed about one-third of the inmates. The other inmates were from Russia, Poland, Czechoslovakia, Hungary, Yugoslavia, France, Italy, and Greece. Romani people were also imprisoned. Most were political prisoners. Mauthausen received the harshest classification of concentration camp after Heydrich decreed that they be classified in 1941. The mortality rate in camps in the Mauthausen group was three times higher than that of other groups.:258
Georg Bachmeier was the camp's first commander for a few weeks. Anton Bentele or Bendele was the next camp commander, until the start of 1944, when SS Obersturmführer Otto Riemer became camp commander. Prisoner accounts report that Reimer beat, tortured, and murdered prisoners. After shooting some eight prisoners while drunk, Riemer was demoted and transferred to the Gusen concentration camp post office. Anton Ganz replaced him. One surviving prisoner described Ganz as "brutal, arbitrary, dictatorial and crude.":14–16 Harrmann Pribill, an SS Unterscharführer, distributed work and determined work details.:16