The organisation of the security-intelligence system of the future communist Yugoslavia began in 1941 within the framework of Partisan movement. The formal date for the establishment of an intelligence service has been set 13 May 1944, when the People’s Protection Department (Odjeljenje za zaštitu naroda – OZNA) was formed. After promulgation of the 1946 Yugoslav Constitution on January 31, it was reorganised by its division into civilian and military services. A part of the OZNA, Section II, which was engaged in security and counterintelligence activities, was renamed the State Security Administration (Uprava državne bezbjednosti – UDBA), and on 13 March 1946 it was moved from the National Security Ministry of the Federal People’s Republic of Yugoslavia (FPRY) and placed under the authority of the Internal Affairs Ministry of the FPRY (Radelić 2015, p. 96). After the Fourth Plenum of the Central Committee of the League of Communists of Yugoslavia, held on in Brijuni on 1 July 1966 (the Brijuni Plenum), the UDBA in Croatia was renamed the State Security Service of the Republic Internal Affairs Secretariat of the Socialist Republic of Croatia (Služba državne sigurnosti Republičkog sekretarijata za unutrašnje poslove SRH – SDS RSUP SRH), and was indirectly subordinated to the Federal Internal Affairs Secretariat (Savezni sekretarijat unutarnjih poslova – SSUP). Until then, it was under the exclusive jurisdiction of the federal authorities. According to the Amendment to the Internal Affairs Act passed on 18 April 1991, the activities of the State Security Service were assumed by the Service for the Protection of the Constitutional Order, which – as noted on the website of the Security and Intelligence Agency of the Republic of Croatia – “developed into a modern service which did not target citizens of opposing political views, either legally or in practice, but rather protected the constitutional order in the entire territory of the Republic of Croatia against unconstitutional and illegal acts.”

The security-intelligence system in communist Yugoslavia/Croatia was primarily under the control of the Communist Party (Radelić 2015, p. 80), so the Party’s organs played the key role in the organisation of the intelligence and counterintelligence services. According to Radelić, besides establishing more effective security against enemies and gathering military intelligence, the Communist Party of Yugoslavia was the security-intelligence system of the Partisan movement, having fostered from the very outset the unification of Party and state authority in line with its revolutionary objectives (Radelić 2015, p. 104). Full control over the security-intelligence services was a key precondition of the CPY's successful confrontation with members of hostile armies and movements, rival parties and individuals in its struggle to take over the government, restore Yugoslavia and reorganise it in accordance with the Marxist ideology of a classless society (Radelić 2015, 74-75).

This was also the conclusion of G. Akrap, who observed that the Yugoslav security-intelligence system was fully in the service of achieving goals and tasks which complied with the “Party line” and commissioned by the political and military leadership. It was a stringently centralized system controlled by top Party officials. It had executive and repressive authority (expulsion, displacement, resettlement, filing charges, arrests, imprisonment, torture, liquidation), as well as organisational units in charge of the organised elimination of all political opponents. This was accompanied by a hiring policy according to which the service was staffed by persons most loyal to the Communist Party (Akrap 2016, pp. 59-63). In Party documents from the initial post-war period, the UDBA was characterized as an authority charged with the protection of legality, belying the inhumane features of its activities.

As described by D. Mikšić, the key transmission point in the structure and jurisdiction of the Service was already mentioned during the Brijuni Plenum held in 1966, when irregularities were detected, followed by a reorganisation of the Service. The newly established republican centres and SDS centres were modelled after the federal SDS organisation. It developed an organisational network via the republican internal affairs secretariats, and they in turn set up their own through SDS centres and territorial branches. The SDS centre for Croatia was in Zagreb, and there were also 10 regional centres: Bjelovar, Gospić, Karlovac, Osijek, Pula, Rijeka, Sisak, Split, Varaždin and Zagreb, as well as branch offices in Dubrovnik, Slavonski Brod, Šibenik, Vinkovci and Zadar. The operational level within the SDS was covered by a network of intelligence operatives and their sources: informants and associates. The SDS had several directorates, i.e., departments. Four main directorates dealt with domestic enemies, enemy émigrés, foreign intelligence agencies and surveillance and wiretapping techniques (Emigration. A guide through the funds and collections of the Croatian State Archives, p. 406).

The internal by-laws of the State Security Service of 30 January 1967 stipulate that its core activities are the collection, documentation, recording and analysis of data to detect and prevent covert and organised enemy activities by foreign intelligence agencies, Yugoslav émigrés, individuals, groups and organisations at home and abroad aimed at undermining and disrupting the constitutional order (Leljak 2016, 377-378).