Second World War had slowed expansion significantly, but the network was in length with each of the three companies – unusually for an underground network – continuing to run their respective lines, which were financed entirely with private capital, unlike the country's railways which had been largely dependent on subsidies. Nationalisation The entire network was centralised and nationalised in 1939 under the management of the Transport Corporation of Buenos Aires (CTCBA) and the lines were given their current lettered naming scheme, from A to D in the order in which the lines were opened. In 1952, the CTCBA was absorbed by the Buenos Aires Transport General Administration (AGTBA), and in 1963, the administration was dissolved and the underground network became the property of the Subterráneos de Buenos Aires company (SBA). In the early years of nationalisation, interchanges were provided between the lines previously belonging to the three different companies that built them (AATC, CHADOPyF and Lacroze) since previously only the CHADOPyF lines (C, D and E) had formal connections between them. However, the rate of expansion of the network during this period had slowed considerably and only one station was opened during the 1970s. Four different long-term expansion proposals were put forward between 1964 and 1991 which all proposed adding numerous lines to the network as well as extending the existing ones. Given the political instability characteristic of Argentina during this time, none of these proposals came to fruition, though aspects of them have been incorporated into contemporary expansion plans. One additional proposal put forward in 1973 saw the unification of the city's commuter rail lines through tunnels and incorporated into the Buenos Aires Underground, and while this was also shelved, it was included in the Red de Expresos Regionales proposal. During the 1960s and 70s, efforts were primarily concentrated on Line E, which was re-routed from its terminus at Constitución to the centre of the city at the Plaza de Mayo in an attempt to boost passenger figures, something which proved to be successful. The segment was opened by president Arturo Illia in 1966 and Spain offered CAF-General Eléctrica Española trains in order to cancel part of the debt it had accrued with Argentina; trains which continue to serve on the line today. The line was extended westward to José María Moreno in 1973, in what would be the only expansion of the decade. In 1979, SBA became Subterráneos