Nazi concentration camp in southern Germany. Erected in 1933, this was the first Nazi concentration camp. Used mainly to incarcerate German political prisoners until late 1938, whereupon large numbers of Jews, Gypsies, Jehovah's Witnesses, homosexuals, and other supposed enemies of the state and anti-social elements were sent as well. Nazi doctors and scientists used many prisoners at Dachau as guinea pigs for experiments. Dachau was liberated by American troops in April 1945.