Complex sentence: Despite this, he still lost contact with the leading 23rd Battalion which quickly overwhelmed its opposition and advanced so quickly that it arrived at its final objective so far ahead of schedule that it believed it had only reached its first objective and so advanced even further.
Split into simpler sentences: Despite this, he still lost contact with the leading 23rd Battalion which quickly overwhelmed its opposition. In fact, the battalion had advanced so quickly that it arrived at its final objective so far ahead of schedule that it believed it had only reached its first objective and so advanced even further.