Buchenwald first opened to male prisoners in July 1937. Women were not part of the Buchenwald camp system until 1944. Prisoners were confined in the northern part of the camp in an area known as the main camp, while SS barracks and the camp administration compound were located in the southern part. The main camp was surrounded by an electrified barbed wire fence, watchtowers, and a chain of sentries outfitted with automatic machine guns. The jail, also known as the bunker, was located at the entrance to the main camp. The SS carried out shootings in the stables and hangings in the crematorium area.
Most of the early inmates at Buchenwald were political prisoners. However, in 1938, in the aftermath of Kristallnacht, German SS and police sent almost 10,000 Jews to Buchenwald where they were subjected to extraordinarily cruel treatment. 600 prisoners died between November 1938 and February of 1939. Beginning in 1941, a varied program of medical experiments took place at Buchenwald in special barracks in the northern part of the main camp. Medical experiments involving viruses and contagious diseases such as typhus resulted in hundreds of deaths. In 1944, Dr. Carl Vaernet began a series of experiments he claimed would "cure" homosexual inmates. Also in 1944 a "special compound" for prominent German political prisoners was established near the camp administration building in Buchenwald. Ernst Thaelmann, Chairman of the Communist party in Germany before Hitler's rise to power in 1933, was murdered there in August 1944.
The prisoner population at Buchenwald expanded rapidly, reaching 110,000 by the end of 1945. Prisoners were used in German Equipment Works, an enterprise owned and operated by the SS, in camp workshops, and in the camp's stone quarry. In March of 1943 the Gustloff firm opened a large munitions plant in the eastern part of the camp. A rail siding completed in 1943 connected the camp with the freight yards in Weimar, facilitating the shipment of war supplies.
Buchenwald administered at least 87 subcamps located across Germany, from Dusseldorf in the Rhineland to the border with the Protectorate of Bohemia and Moravia in the east. Prisoners in the satellite camps were put to work in armaments factories, stone quarries, and on construction projects. Periodically the prisoners at Buchenwald underwent system selection. The SS staff sent those too weak or disabled to continue working to the Bernburg or Sonnestein euthanasia killing centers, where they were killed by gas. Other weakened prisoners were killed by phenol injections administered by the camp doctor.
As Soviet forces swept through Poland, the Germans evacuated thousands of concentration camp prisoners from western Poland. After long, brutal marches, more than 10,000 weak and exhausted prisoners from Auschwitz and Gross-Rosen, most of them Jews, arrived in Buchenwald in January 1945.
In early April of 1945, as American forces approached the camp, the Germans began to evacuate some 28,000 prisoners from the main camp and an additional 10,000 prisoners from the subcamps of Buchenwald. On April 11, 1945, starved and emaciated prisoners stormed the watchtowers, seizing control of the camp. Later that afternoon American forces entered Buchenwald. Soldiers from the U.S. 3rd Army division found more than 20,000 people in the camp, 4,000 of them Jews. Approximately 56,000 people were murdered in Buchenwald, the majority of them after 1942.
