SDB organization was constantly changing and making improvements, but it remained tied to the central unit in republic capitals and smaller working groups in the field. All information and data flowed into the central unit in the capitals and sent on from there to the users. Field groups had working contacts with the local authorities, but did not answer to them. Activities 1946–1986 period One of the first successful actions of UDBA was operation Gvardijan, that denied Božidar Kavran the chance to infiltrate ex-Ustasha groups in order to start an uprising against Yugoslavia, eventually capturing Kavran himself. From 1963 to 1974, security intelligence services dealt with a series of domestic and foreign political events. At home, there were political confrontations both before and after the Brioni Plenum (1966), liberal flareups and massive leftist student demonstrations in Belgrade in 1968, Hrvatsko proljeće (Croatian Spring) or "MASPOK" (mass movement) in Croatia in 1971, a nationalist incursion of the Bugojno group in the Raduša area (1972), and a revival of nationalism in Yugoslav republics. The most significant event abroad was the invasion of the Warsaw Pact troops of Czechoslovakia in 1968. These were the circumstances at the time the first act on internal affairs of the individual republics was adopted in 1967. According to this act, internal affairs were handled directly by the municipal administrative bodies and the secretariats of internal affairs of each republic or by their provincial bodies. This was the first time since 1945 that republics gained control and greater influence over their individual security organs and intelligence security services. The State Security Service (SDB) was defined by law as a professional service within the Republic Secretariat of Internal Affairs (RSUP). Naturally, most of its competence remained within federal institutions, as prescribed by the Act on Handling Internal Affairs Under Competence of Federal Administrative Bodies (1971), which determined that the federal secretariat of internal affairs would coordinate the work of the SDB in the republics and provinces. Further steps were taken with the transformation of the state administration, adoption of the Federal Act on State Administration (1978), and the Republic Act (1978). The newly adopted act on internal affairs tasked the Republic Secretariat of Internal Affairs (RSUP) with state security issues, which then became RSUP issues and were no longer given special handling "at the RSUP". This resolution remained in force until the 1991 modifications of the act on internal