Summary/Abstract: After 1903 a number of guerrilla groups were established in the territory of Old Serbia. These activities, which are conditionally called the Chetnik action, flourished until 1908. The Young-Turk revolution, frequent Albanian uprisings and increasingly intensive repression over the Serbian population in these territories paralyzed guerrilla actions. The creation of the Balkan union, accelerated preparations for war and the situation in the field influenced the new approach to organizing and acting of guerrilla groups, which based on a wide institutionalized foundation. Various parts of official military and civil structures were included in these activities. Since 1911, a new approach to guerrilla problems was applied. A special center for the training of guerrilla fighters was established in the town of Prokuplje. The training was conducted by Serbian officers who were on leave or who were resigning. In the vicinity of the border with Turkey special intelligence centers were established, which were run by the officers experienced for such work. A newly formed secret organization Union or Death, which gathered mostly officers but also industrialists, bankers and journalists, gradually united its work with the National Defense directing it towards assistance to guerrilla groups. Just before the beginning of the war, the Serbian general staff sent several groups of general staff officers to get acquainted with the circumstances in the field, get connected with guerrilla groups and introduce their commanding officers to the details of the Serbian war plan, but also to establish contacts with the leaders of the Albanian guerrilla groups and try to win them over to participate in war on Serbian side. Several big guerrilla companies were formed with the task to act from the flanks of the Serbian troops and to fight as their advance party. These squads were parts of the Third Army. Along the directions of action of the First Army units there were two squads operating, which were active before the war already, and their participation in military actions during the war was prominent. Gradually, the guerrilla squads were loosing their traditional characteristics, merging with the regular units of the Serbian army. They reactivated at the beginning of the World War I under new circumstances.
