 On the night of the Chinese counteroffensive , the PVA 120th Division first accidentally stumbled upon the US 9th Infantry Regiment on the northern bank of the Ch 'ongch 'on River . The surprise encounter between the two sides soon left the 9th Infantry Regiment with only three rifle companies combat effective . Unaware that the 1st Battalion of the US 23rd Infantry Regiment had pulled up behind the US 61st Field Artillery Battalion , four Sharp Sword Companies from the PVA 359th Regiment of the 120th Division proceeded to cross the river and attacked the US artillery positions . Although the 61st Battalion was routed by surprise , the US 23rd Infantry Regiment quickly knocked out two of the unsuspecting Chinese companies . The surviving Chinese troops drifted eastward and occupied a hill named Chinaman 's Hat , enabling the Chinese to overlook the entire 23rd Infantry Regiment 's positions . 
