The armaments factory adjacent to the camp, the so-called Gustloff-Werk II, begins production with an inmate workforce. The construction of a railway line to Weimar gets underway. Inmates are forced to build it in only three months. Large subcamps are built at the Erla-Maschinenwerk GmbH in Leipzig, the Junkers Flugzeugwerke in Schönebeck and the Rautalwerke Wernigerode to house Buchenwald inmates working in the armaments industry. Large transports of Polish inmates arrive from the Auschwitz and Majdanek concentration camps.
The thirteenth series of experiments on inmates is carried out in block 46, now with epidemic typhus remedies produced by the Hoechst company. More than half of the subjects die a painful death during the experiment.
Members of the French government, among them the former prime ministers Édouard Daladier, Paul Reynaud and Léon Blum, are interned in the SS falcon lodge as special inmates. Léon Blum remains there until April 1945.
The first major transport arrives from the Compiègne transit camp in Northern France.
The "Dora" subcamp is established near Nordhausen in preparation for underground rocket production. In the first six months of the tunnel construction, 2,900 inmates die. The first major transports from Ukraine arrive in Buchenwald.
The camp inmate population has increased to 37,319. This number includes 14,500 Russians, 7,500 Poles, 4,700 French and 4,800 Germans and Austrians. Nearly half are in subcamps. In 1943, 3,862 inmates have died in the Buchenwald camp complex.