A professional soldier on the outbreak of World War I, Ravenstein fought as an infantry officer on the Western Front. Awarded the Pour le Mérite in 1918, he participated in the border disputes with Poland after the war before leaving the military. After attending university, he obtained employment with an electrical company and then later with the Duisburg city administration. In 1934, he joined the "Heer" (Army) branch of the Wehrmacht. He led a rifle regiment in the Invasion of Poland and the Battle of France. In May 1941, he was appointed commander of the 5th Light Division, at the time operating in North Africa. His command was soon redesignated as the 21st Panzer Division. He was captured by soldiers from the 2nd New Zealand Division during the British Eighth Army's Operation Crusader.