Complex sentence: He was also a recipient of the Knight's Cross of the Iron Cross with Oak Leaves, which, especially its higher grade Oak Leaves, was awarded to recognise extreme battlefield bravery or successful military leadership.
Split into simpler sentences: He was also a recipient of the Knight's Cross of the Iron Cross with Oak Leaves. The Knight's Cross of the Iron Cross and its higher grade Oak Leaves was awarded to recognise extreme battlefield bravery or successful military leadership.