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German Fahrschulwanne
The German Army needed vehicles to train tank crew drivers but the big problem was fuel. Diesel and gasoline were required for front line vehicles and there was a massive shortage with no solution in sight. German engineers looked for an alternative fuel source. They came up with two solutions. One was a device that burnt wood and produced combustible gas that could power an engine. The other was to use compressed gas bottles that contained gas similar to that supplied to homes in Germany for cooking.
These vehicles were called "Fahrschulwanne". This is a term used by those who were trained on these vehicles and a combination of "Fahrschule" (Driving school) and the German term "Wanne". This does not mean the lower hull of a tank but is malapropism of the term "Badewanne" (Bathtub). Thus the term 'Fahrschulpanzer' translates to 'Driving School Tank'. Fahrschulepanzerjäger would mean Tank-Destroyer-Training-school-vehicle.
Wood Gas powered tanks – Holzgas
The commercial term for a wood gas generator, or Holzkohevergaser in German, was the Imbert-holz-gas system which then was shortened to Holzgas. The gas was used to fuel vehicle engines thus saving on petrol/gasoline and diesel. The Imbert system is a closed external combustion system designed to produce gas that can be cooled and used in an internal combustion engine.
The Imbert system uses wood pellets and the gas produced needs cleaning and cooling prior to passing to the cylinders of the vehicle, otherwise it would choke up with residue. During the production process, biomass or other carbon-containing materials are gasified within the oxygen-limited closed environment of a wood gas generator to produce hydrogen and carbon monoxide.
In Germany, around 500,000 gas powered vehicles were in use at the end of the war due to the lack of petroleum.