The troops from the various territories of Elector Frederick William had traditionally been in separate commands. In 1651, the elector granted Sparr command over all garrison troops outside of Brandenburg and the Duchy of Prussia; command over all of Brandenburg-Prussia's troops followed in 1655. Sparr acted as Frederick William's Chief of Staff when the elector personally led troops, such as at the 1656 Battle of Warsaw. During the final day of the battle, "Generalfeldzeugmeister" (Master of Ordnance) von Sparr led Brandenburg's successful assault on the Polish forces. He was promoted to Field Marshal in 1657.