"Swiss miracle"—was a development of the short 20th century, among other things tied to the role of Switzerland during the World Wars. Germany considered invading Switzerland during World War II but never attacked. Under General Henri Guisan, the Swiss army prepared for the mass mobilization of militia forces against invasion and prepared strong, well-stockpiled positions high in the Alps known as the Réduit. Switzerland remained independent and neutral through a combination of military deterrence, economic concessions to Germany, and good fortune as larger events during the war delayed an invasion. Attempts by Switzerland's small Nazi party to cause an Anschluss with Germany failed miserably, largely due to Switzerland's multicultural heritage, a strong sense of national identity, and long tradition of direct democracy and civil liberties. The Swiss press vigorously criticized the Third Reich, often infuriating German leaders. Switzerland was an important base for espionage by both sides in the conflict and often mediated communications between the Axis and Allied powers. Switzerland's trade was blockaded by both the Allies and the Axis. Both sides openly exerted pressure on Switzerland not to trade with the other. Economic cooperation and extension of credit to the Third Reich varied according to the perceived likelihood of invasion, and the availability of other trading partners. Concessions reached their zenith after a crucial rail link through Vichy France was severed in 1942, leaving Switzerland surrounded by the Axis. Switzerland relied on trade for half of its food and essentially all of its fuel, but controlled vital trans-alpine rail tunnels between Germany and Italy. Switzerland's most important exports during the war were precision machine tools, watches, jewel bearings (used in bombsights), electricity, and dairy products. During World War Two, the Swiss franc was the only remaining major freely convertible currency in the world, and both the Allies and the Germans sold large amounts of gold to the Swiss National Bank. Between 1940 and 1945, the German Reichsbank sold 1.3 billion francs worth of gold to Swiss Banks in exchange for Swiss francs and other foreign currency. Hundreds of millions of francs worth of this gold was monetary gold plundered from the central banks of occupied countries. 581,000 francs of "Melmer" gold taken from Holocaust victims in eastern Europe was sold to Swiss banks. In total, trade between Germany and Switzerland contributed about 0.5% to the German war effort but did not significantly lengthen the war. Over the course