Of the 77 fighters who formed the first Partisan unit, 38 survived the war. Most of them were from the wider area of Sisak and were mainly members of the Communist Party. They set up the unit on 22 June 1941 when Nazi Germany attacked the Soviet Union despite the previously signed Molotov–Ribbentrop non-aggression pact.
Three distinguished members of the Sisak Partisan Detachment were its commanders Vlado Janjic-Capo and Marijan Cvetkovic, as well as Janko Bobetko, who was later a general of the Croatian Army during the 1991-1995 Homeland War.
An estimated 500,000 Croatians participated in the antifascist resistance movement during the Second World War, including 230,000 armed fighters.
After it gained independence from the Socialist Federal Republic of Yugoslavia, Croatia started observing Antifascist Struggle Day on 22 June as a public holiday.
The main commemoration is organised by the Croatian Alliance of Antifascist Fighters and Antifascists and the Sisak city authorities in Brezovica Forest every year.