Knin police chief Milan Martić established paramilitary militias. The two men eventually became the political and military leaders of the SAO Krajina, a self-declared state incorporating the Serb-inhabited areas of Croatia. The JNA learned about Croatia's intention to develop its own military force from JNA Captain Vladimir Jager, a double agent employed by Croatia and the JNA Counterintelligence Service (KOS). The JNA devised Operation Shield (Štit), aimed at disarming the Croatian forces and the arrest and trial of the Croatian leadership, in response. Although the operation was prepared by December 1990, federal Defence Minister General Veljko Kadijević never sought authorisation to carry it out from the Yugoslav Presidency. Instead, he ordered the KOS to stand down on the morning the operation was scheduled to begin. At the beginning of 1991 Croatia had no regular army, and to bolster its defence Croatia doubled the size of its police force to about 20,000. The most effective part of the force was the 3,000-strong special police, deployed in a military organisation of 12 battalions; in addition, there were 9,000–10,000 regionally-organised reserve police officers. Although the reserve police were set up in 16 battalions and 10 companies, they lacked weapons (which were needed to arm the troops). History Establishment Preparations for the ZNG began on 12 April 1991. Its formation as a police force with military capability was considered necessary by Croatian authorities after March clashes in Pakrac and at Plitvice Lakes and the possibility of further confrontation with the JNA. Since it was illegal to establish a separate military in a constituent republic of Yugoslavia, the ZNG was planned as part of the police force under the Ministry of the Interior. Parliament amended the Internal Affairs Act on 18 April, and the ZNG was formally established five days later. It was tasked with the protection of the constitutional order, the maintenance of public order, anti-terrorist operations, the protection of Croatia's borders, territory, coast and territorial waters, valuable structures and high-profile individuals. Although the ZNG was formally subordinate to the Ministry of the Interior, its founding legislation stipulated that it would be commanded by the Ministry of Defence. On 5 May the number of ZNG troops and their composition was determined, followed by operational guidelines issued by Defence and Interior Ministers Martin Špegelj and Josip Boljkovac for the transfer of police personnel to the ZNG on 10 May. By 15 May several special police