Complex sentence: Schmidt was awarded the Knight's Cross for his battalion's succesful defence in the Isjum sector, which was followed by him leading his battalion out of the Cherkassy pocket for which he was promoted to Hauptsturmführer and awarded the Oakleaves to the Knight's Cross.
Split into simpler sentences: Schmidt was awarded the Knight's Cross for his battalion's succesful defense in the Isjum sector. After defending the Isjum sector, he led his battalion out of the Cherkassy pocket, for which he was promoted to Hauptsturmführer and awarded the Oakleaves to the Knight's Cross.