The most important factor contributing to the "Tegetthoff"s spending most of their time at port may have been the lack of coal. Prior to the war, the United Kingdom had served as Austria-Hungary's primary source for coal. In the years before the war an increasing percentage of coal had come from mines in Germany, Virginia in the United States, and from domestic sources, but 75% of the coal purchased for the Austro-Hungarian Navy came from Britain. The outbreak of war meant that these sources, as well as those from Virginia, would no longer be available. Significant quantities of coal had been stockpiled before the war however, ensuring the navy was capable of sailing out of port if need be. Even so, the necessity of ensuring the navy's most important ships such as the "Tegetthoff"s had the coal they needed in the event of an Italian or French attack or a major offensive operation resulted in the dreadnoughts remaining at port unless circumstances necessitated their deployment at sea.