A nice review of this library footnote to World War II. The Germans captured all the geological, hydrological and terrain maps available from the private, public and univeristy libraries of the countries they invaded. Near the end of the war, these maps were hidden in a salt mine near Heringen, Germany, where they were then captured from the Germans by the US Army. They are still in use today in a number of American libraries.

An account of the discovery of a collection of captured maps, reports and data in a salt mine near Heringen, Germany, at the end of World War II. These geological and hydrological maps had been confiscated by German army geologists, Wehrgeologenstellen, as the armies invaded other countries. Hidden in a salt mine in central Germany in 1944, they were discovered by General Patton's 3rd Army in March 1945, and most of the items eventually ended up at the US Geological Survey Library, where they are still used today. ( )

See: http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_64921.htm