Complex sentence: The 1st Battalion was emplaced with the 2nd Battalion but stayed less than 24 hours before it was sent to reinforce the US 27th Infantry Regiment on the next north-south line of communications westward.
Split into simpler sentences: The 1st Battalion emplaced with the 2nd Battalion but stayed less than 24 hours. It had been immediately sent to reinforce the US 27th Infantry Regiment on the next north-south line of communications westward.