By late-July, South Korea was reduced to the southeast tip of the peninsula around Pusan, held by the United Nations Command (UNC) forces, mainly the US Eighth Army, and the ROK.

Korean transportation infrastructure was heavily damaged by the war and, combined with most principle routes being in the north–south direction due to the mountainous terrain, he may have believed supplying a quick advance by both Eighth Army and X Corps from Inchon to be impossible.

A message dropped by a Korean Military Advisory Group (KMAG) G-3 officer from a light plane at Samch'ok and delivered to Colonel Emmerich at Kangnung on the afternoon of 29 September ordered the ROK 3rd Division to cross the 38th Parallel and proceed to Wonsan as soon as possible.

The ROK 3rd Division traveled northward night and day, on foot and by vehicle, out of communication most of the time with higher headquarters, without flank protection to the west, and bypassing many KPA groups which often attacked their supply points in the rear.

During the night a KPA armored task force, including about ten 76 mm self-propelled antitank guns, returned to the airfield and did a good job of shooting it up, burning out most of the buildings and hangars.

After it turned west from the Sibyon-ni road the 5th Cavalry encountered an almost continuous minefield in its approach to Kumch'on, and it also had to fight and disperse a KPA force estimated to number 300 soldiers, 13 km (8 mi) from the town.

In a series of conferences from 2 to 4 October, Struble and his staff decided to form the Advance Force JTF 7, which would proceed to the objective area and begin minesweeping at the earliest possible date.

[57] The menace of shore batteries was removed on 17 October when ROK I Corps, which had already captured Wonsan, gained control of the peninsulas and islands commanding the harbor approaches, however, casualties from mines continued.

[71] In order to stabilize the rapidly collapsing Korean front and to push back the advancing UN forces, Mao authorized the First Phase Campaign, a bridgehead-building operation with the aim of destroying ROK II Corps, the vanguard and the right flank of the Eighth Army.

Allen had been in the command post of the 2nd Battalion, 187th RCT, only a short time when a Korean civilian came in and excitedly told a story of KPA troops murdering about 200 Americans the night before at a railroad tunnel northwest of the town.

Two trains, each carrying about 150 American prisoners of war, had left Pyongyang on the night of 17 October, making frequent stops to repair the tracks, and crawling north at a snail's pace.

The 3rd Engineer Combat Battalion now worked to clear the highway to Sinanju, and to improve it for carrying the main part of Eighth Army's logistical support in the projected drive to the Manchurian border.

[80] Until 17 October MacArthur's orders, based on the Joint Chiefs of Staff directive of 27 September, had restrained UN ground forces other than ROK troops from operating north of a line extending from Ch'ongju on the west through Kunu-ri and Yongwon to Hamhung on the east coast.

When the 27th British Commonwealth Brigade crossed the Ch'ong-ch'on, that unit, the US 24th Infantry Division which followed, and all the other UN troops deployed in Korea, were authorized to go to the Yalu River —to the extreme northern limits of the country.

The Suiho hydroelectric dam on the middle Yalu impounds a reservoir of the same name that extends upstream for 100 km (60 mi), pushing water into hundreds of little lateral fjordlike mountain valleys.

The Reconnaissance Platoon from the 7th Regiment, ROK 6th Division, was the first UN unit to reach the northern border of North Korea, and, as events turned out, it was the only element operating under Eighth Army command ever to get there during the war.

At the same time, thirty B-29's dropped 40,000 incendiary bombs on Hoeryong, a rail and road communication center of 45,000 population on the Tumen River at the Manchurian border, 161 km (100 mi) southwest of Vladivostok.

The 32nd Infantry, which began unloading on 4 November and was the last of the regiments to come ashore at Iwon, moved southwest from the beach along the coast through Hamhung and there turned northeast to Tangp'ang-ni in preparation for its part in the operation.

To replace the bridge which the North Koreans had blown, Colonel Powell had ROK troops in the regiment construct a floating footbridge made of planking extending between empty oil drums.

In this action the 17th Tank Company overran KPA troops in their foxholes, while the heavy fire of the 15th Anti-aircraft Artillery Battalion 40mm weapons drove other North Koreans from log-covered trenches and pillboxes and then cut them down.

Leaving strong detachments to guard the mountain passes from the reservoir eastward into the division's rear along the Cho-ri-P'ungsan road, General Barr on 20 November began moving the bulk of the 31st and 32d Regiments to the P'ungsan-Kapsan area behind the 17th Infantry.

This set a pattern of action that occupied the 17th Infantry during the next week, daily fights with small but stubborn enemy forces that blew bridges, cratered roads, all but immobilized the regiment, and kept it from making any appreciable gains.

Information gained later from prisoners disclosed that the artillery and mortar barrage against How Hill during the night had caused crippling casualties in the 372nd Regiment (possibly the 371st) of the 124th Division while it was moving up to reinforce the line.

General Almond meanwhile had ordered Colonel Harris, commanding officer of the 65th Infantry Regiment, 3rd Division, to place one battalion near the boundary to establish contact there with elements of Eighth Army.

[114] On 15 November MacArthur instructed Almond to open an attack to the west after his inland flank forces reached the town of Changjin, 40 km (25 mi) north of the Chosin Reservoir.

Almond intended that the 1st Marine Division make the westward effort into Mup'yŏng-ni and then press an attack northwestward to the Yalu, pinching out in the process ROK II Corps on the Eighth Army right.

[1]: 59–60 While General Walker fully expected the Eighth Army to encounter Chinese when it moved north, the lack of revealing contact in his zone left him uncertain about the location of PVA/KPA positions.

On the Corps' right, two regiments of Maj. Gen. Paik Sun Yup's ROK 1st Division supported by a company of American tanks advanced on T’aech’on, moving upstream on both sides of the Taeryong River over secondary roads that converged on the objective 16 km (10 mi) northwest.

Rather than risk an open west flank, General Keiser ordered short moves by his line regiments, the 9th and 38th, to mass along the lower bank of the Paengnyong River, a westward flowing tributary of the Ch’ongch’on.

The ROK 1st Division, on the other hand, had found during the night that T’aech’on would be harder to take when PVA supported by artillery and mortar fire counterattacked along the east bank of the Taeryong and forced part of General Paik's right regiment 3 km (2 mi) to the rear.