the Swiss Armed Forces staff at the founding site of the Swiss confederation, that in case of attack the Swiss would only defend the high Alps including the important transalpine roads and rail links. As a last resort, the army would make these routes useless to the Axis by destroying key bridges and tunnels. This plan, known as the National Redoubt, meant that the populated lowlands – including the economic centres of the country – would effectively be ceded to the Germans and to the Italians. The gold reserves of the Swiss National Bank in Zürich were moved farther away from the German border, to the Gotthard Pass and to Bern. Many billions of Swiss francs have been invested in building the fortifications in the mountains, which are partly still used by the army. The most important buildings of the Reduit were the fortifications of Sargans, St. Maurice (Valais) and the Gotthard region. The caverns of those time were equipped with the needed infrastructure; beside cannons and howitzers they consisted of dormitories, kitchens, field hospitals, rooms for the sick and bakeries; and they provided space enough to accommodate 100 to 600 soldiers for a timespan of up to several months. Because the tensions between the western countries and the USSR cooled down and bunkers became more or less obsolete because of newer weapon systems, a great number of the Reduit buildings were closed. Some of them have been reopened as museums and can be visited. Cold War At the end of the 1950s, reflecting both the threat of possible invasion by the Soviet Union and the realities of nuclear warfare, Swiss military doctrine changed to mobile defense that included missions for the air force outside of its territory, in order to defeat standoff attacks and nuclear threats, including the possibility of defensive employment of air-delivered nuclear weapons. However the inability to field an air force of sufficient capability to carry out such missions led to a return of traditional "protection of own territory" doctrine. Meanwhile, the Air Force also began to prepare ad hoc airbases in the mountains, with sections of highway strengthened to act as runways and hangars carved out of the mountains. In the 1960s and 1970s, the armed forces were organised according to the "Armee 61" structure. During the Cold War, Swiss authorities considered the construction of a Swiss nuclear bomb. Leading nuclear physicists at the Federal