After the First Battle of Naktong Bulge , the US Army 's 2nd Infantry Division was moved to defend the Naktong River line . The division , which was untried in combat , was struck with a strong attack by several divisions of the Korean People 's Army which crossed the river and struck all along the division 's line . The force of the attack split the US 2nd Infantry Division in half , and the North Koreans were able to penetrate to Yongsan , promoting a fight there .