Complex sentence: While they worked, the division's three infantry regiments--9th, 38th and 23rd--launched coordinated assaults on Heartbreak Ridge and the adjacent hills.On 10 October the sudden onslaught of a battalion of tanks racing up the valley took the enemy by surprise.
Split into simpler sentences: While they worked, the division's three infantry regiments--9th, 38th and 23rd--launched coordinated assaults on Heartbreak Ridge and the adjacent hills. The sudden onslaught of a battalion of tanks racing up the valley took the enemy by surprise.