The battle of Castle Itter (Schloss Itter in German) was fought on the 5th of May 1945 in the Austrian village of Itter, five days after the suicide of Adolf Hitler.
The castle, a former prison for high-profile political captives of Nazi Germany, was defended by the former prisoners and the Austrian anti-nazi resistance, together with troops from the U.S. Army and a unit of recent defectors from the German Army.
Attacking the newly liberated castle was a force of SS Panzergrenadiers.
It is often cited as (probably) the only battle in World War 2 where American and German troops fought side by side.