The Battle for Castle Itter was a battle fought in the Austrian village of Itterball. The battle is known for the fact that a German division had sided with an American corps and recently freed French prisoners against other Germans. Yes this battle exists.
The battle began following the Germans retreating from Castle Itter, due to a former commander dying under suspicious circumstances and a Yugoslav resistance member not returning from an errand run. Upon leaving, the French prisoners, including former prime ministers, generals, and a tennis star, armed themselves with weapons left behind by the Germans.
The Yugoslav resistance member had actually gotten outside help from an American corps, with a note seeking assistance. A Czech cook also carried the letter to a group of Austrian resistance members and a group of defiant German SS members.
During the inital part of the battle, the troops came across SS troops creating a roadblock. This is where the battle commences.
The Allied side eventually defeated and captured the German troops.