Chetniks in World War I

Chetniks in World War I were irregular auxiliary units of the Royal Serbian Army, active between 1914 and 1918, and tasked with special operations against invading Austro-Hungarian, Bulgarian, and German forces. Although their origins lay in earlier nationalist resistance movements and their formal use during the Balkan Wars (1912–1913), the Serbian Army established four official Chetnik detachments in August 1914.

Initially deployed to defend Serbia's borders, these units soon shifted to guerrilla operations behind enemy lines, engaging in sabotage, ambushes, and diversionary attacks. Following the occupation of Serbia in late 1915, surviving Chetniks reorganised into underground resistance groups, forming new detachments that continued to operate in the occupied territories. They played a significant role in the Toplica uprising (1917) and contributed to the final liberation of Serbia and Montenegro in 1918.

After the war, most Chetnik detachments were demobilised or absorbed into the Royal Yugoslav Army. Some former commanders remained active in nationalist veterans' organisations. The memory and legacy of the First World War Chetniks were later revived, by the Yugoslav Army in the Homeland, the royalist resistance movement, during the Second World War.