In August 1914, at the start of First World War, Bahrfeldt was given command of the 19th Reserve Division, part of the X. Reserve Corps and the 2nd Army. He captured Charleroi on August 22, 1914 and, accused by the Allies of atrocities at Charleroi, in 1925 he was condemned to death "in absentia" by a Belgian court. His division participated in the Battle of St. Quentin and the following Battle of the Marne. He fought in the First Battle of Champagne and in June 1915 he was given command of the 10th Reserve Division and promoted to General der Infanterie. He led his division into the Battle of Verdun and was phased out of the Army in April 1916.