Other Croatian industrial assets utilized by the Germans included the production of brown coal and lignite, cement (major plants in Zagreb and Split), oil and salt. Crude oil production, from fields to the east of Zagreb developed by the American Vacuum Oil Company, only started in November 1941 and never reached a high level, averaging a month in mid-1944. The most important commodities manufactured in Croatia for German use were prefabricated barracks (utilizing the large Croatian timber industry), clothing, dry-cell batteries, bridge construction parts and ammunition (grenades).