Suffering from a lack of supplies and mounting casualties, the regiment was committed to the Battle of Pusan Perimeter as part of a push to force United Nations (UN) troops out of Korea.

[3] All 500 men of the 3rd Battalion were lost just before the war started when their transport was sunk while attacking Pusan harbor by the Republic of Korea Navy.

[7] During this time, North Korean leadership also ordered the creation of large conventional units to act as advance forces for the actual invasion.

[2] Prior to the beginning of the war in June 1950, the 766th completed training and was moved to the front at Yangyang to support the KPA's 5th Division.

[8] The North Korean plan was to conduct amphibious landings in Chongdongjin and Imwonjin on the eastern coast using the 766th Regiment, in conjunction with the 549th Unit.

[2] The combination of the frontal attack and the landings were expected to crush the ROK division and prevent reinforcements from moving in to support it.

[14] 588th Unit was tasked with raiding Pusan harbor, destroying vital facilities to make it impossible for UN forces to land troops there.

The ROK 8th Division, under attack from the front and rear, requested reinforcements but the general North Korean offensive along the 38th parallel[17] meant there were none.

[21] With the ROK army in retreat, the 766th Regiment, 549th Unit, and KPA's 5th Divisions all advanced steadily south along the eastern roads without encountering much resistance.

[16] The 766th Regiment acted as an advance force, attempting to infiltrate further inland as it moved through the mountainous eastern region of the country.

[24] The rugged terrain of the eastern regions of Korea, poor communication equipment, and unreliable resupply lines thwarted the South Korean resistance.

[22] The 5th Division and the two other units began advancing south slowly and cautiously, sending strong reconnaissance parties into the mountains to ensure they would not be threatened from the rear.

[26] On July 10, the 766th separated from the 5th Division and met an advance party of North Korean civilians in Uljin who had been sent to set up a government in the area.

The force continued to occupy the eastern flank, and by July 24 it was advancing from the Chongsong-Andong region and approaching Pohang.

[32] The rugged terrain of the mountains prevented the North Korean forces from conducting the enveloping maneuvers they had used so effectively against other troops, and their advantages in numbers and equipment had been negated in the fight.

[34] However the 766th had suffered significant setbacks at Yongdok, with substantial losses due to American and British naval artillery fire.

[33] Once it arrived in the area, it met heavier resistance from South Korean police and militia operating in armored vehicles.

The Korean People's Army planned simultaneous offensives across the entire Perimeter,[31] including a flanking maneuver by the 766th and the 5th Division to envelop UN troops and push them back to Pusan.

[40] By the beginning of August, the North Korean units operating in the area were getting little to no food and ammunition supply, instead relying on captured UN weapons and foraging for what they could find.

[41] The 766th Regiment specialized in raiding UN supply lines, and effectively mounted small disruptive attacks against UN targets to equip themselves.

[42] At dawn on August 11, one 300-man battalion[43] of the 766th Regiment entered the village of P'ohang, creating a state of alarm among its populace.

[45] Upon hearing of the fall of P'ohang, UN Eighth United States Army commander Lieutenant General Walton Walker immediately ordered naval and air bombardment of the village.

[6] Exhausted and out of supplies, the 766th Regiment moved to Pihak-san, a mountain 6 miles (9.7 km) north of Kigye, to join the shattered KPA's 12th Division.