This building produces and holds one of the major resources of the game: the fuels and lubricants required for the support of infantry and vehicles. It also improves various other structures of your base. The game begins with a level one Fuel Depot. Modernization speeds the production of fuel, and increases the total amount of fuel that you can store.
At the beginning of the war, Germany was actively importing petroleum products from other countries. But once war broke out, the British leveled a naval blockade on Germany. In 1940, Western Europe was seized by the Nazis, along with over 8 million tons of oil products, as well as the entire oil industry of oil-rich areas. However, the blitzkrieg faltered, and it soon became clear that their fuel supplies were sorely lacking. Germany attempted to recover by taking the oil-producing regions of the Caucasus, but failed.