The Yugoslav People's Army (JNA) was initially formed during World War II to carry out guerrilla warfare against Axis occupation. The success of the Partisan movement led to the JNA basing much of its operational strategy on guerrilla warfare. Due to the unique political stance of Yugoslavia in Europe, the strategic planners of the Army expected to face an attack by either NATO or Warsaw Pact forces. Expecting to be badly outmatched, the JNA decided to pursue a guerrilla strategy, which would prove disastrous in the upcoming war, since the JNA found itself in a position of an attacker without local civilian support - the very role they intended for invaders of Yugoslavia.
Still, on paper, the JNA looked like a powerful force with 2,000 tanks and 300 jet aircraft (all either Soviet or locally produced). However, by 1991, majority of this equipment was over 30 years old: the main T-54/55 tank and the MiG-21 aircraft made up 60% and 40% of the tank force and air-force respectively.[citation needed] By contrast, more modern cheap anti-tank (like AT-5) and anti-aircraft (like SA-14) missiles were abundant, which were designed to destroy much more advanced weaponry. Furthermore, the JNA was a multinational force: the political infighting meant that desertion of men (especially educated cadre from Yugoslavia's more developed northern areas) would ruin the Army's effectiveness.[citation needed] With the retreat of the JNA forces in 1992, JNA units were reorganized as the Army of Serb Krajina, which was a direct heir to JNA organization with little improvement. During 1991, an important role in the Yugo/Serb military assault forces was filled by paramilitary units like Beli Orlovi, Srpski Četnički Pokret, etc. that committed numerous massacres against Croat and other non-Serbs civilians.
By contrast to this force, the Croatian Army was in much worse state. At the early stages of the war, lack of military units meant that the Croatian police force would take much of the brunt of fighting - eventually the police would form the core of the new military force - initially named "Zbor Narodne Garde" (ZNG), later "Hrvatska Vojska" (HV) - that was formed in 1990,[citation needed] but not really developed until 1993. Weaponry was always lacking and many units were formed either unarmed or with WW2-era rifles. The Croatian Army had just a handful of tanks (even older WW2 veterans like the T-34) and its air-force was even worse: a few old Antonov An-2 biplane crop-dusters were converted to drop makeshift bombs. However, since the soldiers were defending their homeland the army was exceptionally motivated, and was formed into local fighting units - so people from a village would defend their own village - which meant they were fairly effective in their home grounds. In August 1991, the Croat Army had fewer than 20 brigades, which would grow to 60 by the end of the year through general mobilization which was initiated in October. Seizing of JNA's barracks in the Battle of the barracks would slightly alleviate the problem of equipment shortage. Local volunteers and organizations like HOS were formed early on to ease the problem of lack of units, but were later integrated into the regular army.
By 1995, the Croatian Army would develop into an effective fighting force centered on the elite "Guard Brigades" (eight) and less effective "Home Defence Regiments" and regular brigades (most of which were reorganized into Regiments in 1992). This organization meant that in later campaigns, the Croatian army would pursue a variant of blitzkrieg tactics, with Guard brigades taking the role of punching holes in the enemy lines, while other units simply held the front at other points and completed the encirclement of enemy units.