The Army was created on 1 March 1945, when Chief Commander Marshal Josip Broz Tito converted the underground National Liberation Army and Partisan Detachments of Yugoslavia in the more regular Yugoslav Army.

As commander was named General lieutenant Petar Drapšin, as Political Commissioner Colonel Boško Šiljegović, and as Chief of staff, Colonel Pavle Jakšić.

They destroyed the German XV Mountain Corps, surrounded the LXXXXVII Army Corps and liberated Lika, Hrvatsko Primorje, Gorski Kotar, Istria, part of the Slovenian littoral and Trieste with its surroundings.

The 29th Division also participated in the liberation of the area between Postojna and Ljubljana.

According to Vladimir Dedijer IV Army in its composition have 40,500 Croats, 31,500 Serbs and 18,000 Slovenes.