in Nazi Germany, ambitious plans for a U-Bahn, and a new central railway station, were discussed. Test tunnelling took place, but these plans, too, had to be shelved when the Second World War broke out. Severe war damage caused the Stadtbahn system to be suspended in some areas until 27 May 1945. The redevelopment of stations took until the 1950s. Meanwhile, Vienna was occupied by the four allied powers until 1955, and in 1946 had returned three quarters of the pre-war expanded Greater Vienna to the state of Lower Austria. Two proposals for U-Bahn systems were nonetheless presented, in 1953 and 1954. Increasing car traffic led to cutbacks in the S-Bahn network that were partially made up for by buses. The U-Bahn issue was also politicised: in the 1954 and 1959 city council elections, the conservative Austrian People's Party championed construction of a U-Bahn, but the more powerful Social Democratic Party of Austria campaigned for putting housing first. The city council repeatedly rejected the U-Bahn idea in the late 1950s and early 1960s. Extensions of the Stadtbahn system had always been discussed as an alternative to building a new U-Bahn. But it was not until the late 1960s, when the Stadtbahn and the Schnellbahn were no longer able to adequately serve the ever-increasing public traffic, that the decision to build a new network was taken. On 26 January 1968, the city council voted to begin construction of a basic network (Grundnetz). Construction began on 3 November 1969 on and under Karlsplatz, where three lines of the basic network were to meet, and where central control of the U-Bahn was located. Test operation began on 8 May 1976 on line U4, and the first newly constructed (underground) stretch of line opened on 25 February 1978 (five stations on U1 between Reumannplatz and Karlsplatz). The construction of the Vienna U-Bahn network can be divided into several stages: Initial construction (1969–1982): Basic network (Grundnetz) First, the basic network (Grundnetz) was chosen from the various network designs. During 1967, plans for the U2 were radically reduced and the U3 completely deleted, and the approved basic network was described as a 'closer basic network'. This closer basic network, consisting of the U1, U2 and U4 lines, included: New route between Reumannplatz and Praterstern U2 between Karlsplatz and Schottenring U4 between Hütteldorf and Heiligenstadt, consisting almost entirely of modification and adaptation of the existing Stadtbahn line