Though not widely known, it was never really a secret that the Nazis ran brothels in many concentration camps. But never has there been as comprehensive an account of the fact as in a new book by a German researcher.

"Das KZ Bordell" (The Concentration Camp Brothel) has been hailed as the first comprehensive account of a little-known chapter of Nazi oppression during World War Two.

Robert Sommer’s 460-page book is the result of four years of painstaking research in all 10 former concentration camps where the Nazis ran brothels between 1942 and 1945.

It is based on numerous interviews with a small group of survivors.

According to Sommer, Hitler’s Schutzstaffel, or SS bodyguard, was convinced that forced male laborers would work harder if they were promised sex.

”The women who were recruited for the brothels mostly came from the concentration camps of Ravensbrueck and Auschwitz,” Sommer said.

The German social scientist says about 70 percent of these women were Germans. The rest came from Ukraine, Poland and Belarus.