The battle ended in a victory for the UN after large numbers of US reinforcements destroyed an attacking North Korean division.

On August 5, the Korean People's Army (KPA), 4th Infantry Division crossed the Naktong River in the vicinity of Yongsan, attempting to cut UN supply lines to the north as well as gaining a bridgehead into the Pusan Perimeter.

The battle was a turning point in the war for the KPA, which had seen previous victories owing to superior numbers and equipment.

[2] Advance elements of the 24th Division were badly defeated in the Battle of Osan on July 5, the first encounter between US and KPA forces.

[4] The 24th made a final stand in the Battle of Taejon, where it was almost completely destroyed but delaying KPA forces until July 20.

[7] With Taejon captured, KPA forces began surrounding the Pusan Perimeter from all sides in an attempt to envelop it.

[8] UN forces were pushed back repeatedly before finally halting the KPA advance in a series of engagements in the southern section of the country.

Suffering mounting losses, the KPA force in the west withdrew for several days to re-equip and receive reinforcements.

For most of this span, the Naktong is around 400 metres (1,300 ft) wide and 6 feet (1.8 m) deep, allowing infantry to wade across with some difficulty but preventing vehicles from crossing without assistance.

[17][18] The 24th US Infantry Division, under the command of Major General John H. Church, occupied a region some 16 miles (26 km) long along the Naktong River.

[22] At midnight on the night of August 5–6, 800 KPA soldiers of the 3rd Battalion, 16th Regiment waded across the river at the Ohang ferry site, 3.5 miles (5.6 km) south of Pugong-ni and west of Yongsan, carrying light weapons and supplies over their heads or on rafts.

[22][23] A second force attempted to cross further north but was hit with machine gun and artillery fire, falling back in confusion.

At 02:00 on August 6, the KPA began engaging the forces of 3rd Battalion, 34th Infantry and moved forward after a small fight, attempting to penetrate the lines to Yongsan.

[23] American counterattacks continued into the morning of August 7, but the gains were slow, hampered by the hot weather and a lack of food and water.

The KPA were able to press forward and regain the Cloverleaf Hill and Oblong-ni Ridge, critical terrain astride the main road in the bulge area.

[31] Despite a tenacious attack, the 9th Infantry was only able to regain part of Cloverleaf Hill before intense fighting stalled its movement.

Task Force Hill mounted its attack, but was once again unable to make progress due to the newly established artillery.

[35] Its directive to attack quickly became one to dig in and hold its ground, and by nightfall the entire KPA 4th Division was across the river.

[41] Fighting continued the entire day in a fierce series of attacks and counterattacks in which both sides, already at far reduced strength, inflicted large numbers of casualties.

[43][44] It became a battle of attrition by August 15 as neither the KPA 4th Division nor Task Force Hill were able to get the upper hand in the fight, which in several cases erupted in desperate hand-to-hand combat.

[45] Casualties mounted and a frustrated Walker ordered the 5,000-man 1st Provisional Marine Brigade to the area to turn the tide.

[47] The KPA 4th Division in the meantime was suffering serious logistical setbacks from lack of food, equipment, ammunition and, weapons.

[50] The offensive began at 08:00 on August 17,[51] with US forces unleashing all heavy weapons available to them against the KPA positions; artillery, mortars, M26 Pershing tanks and airstrikes.

[37][55] The division's tactics of cutting off supplies and relying on surprise, which had provided them so much success up to this point, failed in the face of massive US numerical superiority.

[55] Scattered groups of KPA soldiers fled back across the Naktong, pursued by American planes and artillery fire.

[57][58] In their hasty retreat, they left a large number of artillery pieces and equipment behind which the Americans later pressed into service.

Their numerical superiority was gone, and their strategy of attacking supply lines and rear formations of US units was no longer effective without overwhelming numbers.