Complex sentence: The troops of "Leibstandarte" were not slated to go into action until later in the day; xxhausted from the previous week's fighting, many were just starting their day at the outset of the attack and were largely taken by surprise.
Split into simpler sentences: The troops of "Leibstandarte" were not slated to go into action until later in the day. Exhausted from the previous week's fighting, many were just starting their day at the outset of the attack and were largely taken by surprise.