In 1639 he left the army for studies in France. At the age of 19 he was drafted to a Hessian cavalry regiment in Swedish service. He distinguished himself at the Battle of Wolfenbüttel 1641. In the Battle of Breitenfeld in 1642 he was wounded and captured by the enemy, but later rescued. During the remaining part of the Thirty Years' War, Ascheberg fought under Field Marshals Lennart Torstenson and Carl Gustaf Wrangel. He distinguished himself on a number of occasions and was made Cornet in 1644, Captain Lieutenant in 1645 and Rittmeister in 1646.