The German War Machine Needs Fuel
Up until the onset of World War II in 1938, most of Germany's oil and fuel supplies came from three sources: imports from overseas, oil extraction from local oil fields, and the production of German synthetic oil from coal.
Allied blockades prevented the importation of fuel to Germany. This resulted in Germany having to rely on its own resources for fuel. Of course, they utilized fuel from conquered countries, but they also had to rely on coal-to-oil conversion. The process by which coal was converted to oil or synthetic fuel is known as the Fischer-Tropsch process.
Partial oxidation of the coal results in the production of carbon dioxide and monoxide. This is a catalyzed process by which carbon monoxide and hydrogen are converted to variations of liquid hydrocarbons. These hydrocarbons are then refined to produce the resulting German synthetic oil.
However, there was another efficient process of coal-to-oil synthesis. Hydrogenation, a process by which the coal-to-oil conversion is exposed to hydrogen, was found to be an efficient option in comparison to the Fischer-Tropsch process.
The reason for this was because the raw materials needed for the Fischer-Tropsch process was more than what was required for the hydrogenation process. The Fischer-Tropsch fuel had a lower octane than the other, but diesel fuel was satisfactory. Also the Fischer-Tropsch fuel was more expensive than hydrogenation in both running and capital expenses for German synthetic oil.
The bombings of synthetic fuel plants by allied forces in May of 1944 had made a huge impact on Nazi Germany and their war effort.