The 21st Assault Serbian Division (Serbo-Croatian Latin: Dvadesetprva udarna srpska divizija) was a Yugoslav Partisan division formed on Radan mountain on 20 May 1944. It was formed as 1st Serbia Division, but it was renamed on 14 June 1944.^[1] Upon formation it had around 1,000 soldiers in three brigades, those being: the 4th, 5th and 6th Serbia Divisions.^[2] Commander of the division was Miloje Milojević. The division mostly fought against Chetniks and Germans in occupied Serbia.^[1]