[1] On 25 October 1950, the People's Volunteer Army crossed the Yalu River into North Korea and attacked United Nations Forces at the Battle of Onjong.

They were tasked with guarding the left flank of the 17th Infantry Regiment in the mountains toward the Pujŏn-ho (Fusen) Reservoir while the 17th captured Kapsan.

RCT-31 reached the Pujŏn-ho (Fusen) Reservoir on 15 November 1950 and engaged with ~200 Chinese forces which were repulsed with air strikes via a Marine F4U Corsair.

In earlier operations, 7th Division units had become widely spread out and isolated from each other in the rugged, mountainous terrain and primitive road network of the region.

This made it impossible to assemble a full-strength task force in time, or to effectively coordinate its operations with the Marines on the south and western sides of the Chosin Reservoir.

Basic defensive positions were established, but the Americans, not expecting enemy activity, did not set up a tight perimeter with 360 degree security.

"[6] The corps commander then flew back to Hagaru-ri, convinced that RCT-31 was strong enough to begin its attack and deal with whatever "remnants" of CCF forces were in their way.

[7] Although large numbers of Chinese troops were seen moving south all day, on the hills east of the task force position, U.S. officers did not change their view of the situation.

This force then returned to the position they had occupied at Hudong, a small, abandoned village north of Hagaru-ri, about 4 miles (6.5 km) south of RCT-31.

Colonel MacLean decided to pull his lead battalion, the 1/32 Infantry, back into the perimeter of his other units a few miles to the south, to provide a stronger defense.

In addition to the cover afforded by F4U Corsair fighter-bombers, much-needed supplies were dropped by the Air Force Combat Cargo Command.

At times, Captain Stamford found himself directing both air drops from cargo planes and close support strikes over the same radio net.

With the assistance of Marine Corps air support – expertly coordinated by Captain Stamford and without which the task force would have been overwhelmed – RCT 31 fought off heavy assaults by the PLA 80th and 81st divisions for another two days, inflicting severe losses on the communist forces who left hundreds of bodies in the snow around the army position.

The Americans were running low on ammunition, and over half their number had been killed or wounded, including a high proportion of key leaders.

The breakout began on 1 December, greatly aided by Marine F4U Corsairs and Navy Grumman F7F Tigercat twin-engine fighters which strafed and bombed Chinese positions as the American truck column, encumbered with hundreds of wounded and under constant attack, made its way down a gravel road on the east side of Chosin Reservoir.

The march south was interrupted when the Corsairs mistakenly bombed short, spraying the lead platoons of the task force with napalm, killing and burning troops.

In the late afternoon, with light fading, Faith got the column moving again, albeit slowly, until it approached Hill 1221 overlooking the road.

One battalion from the PLA 242nd Regiment had set up a strong defensive position on the Hill and a roadblock beneath it to block Faith's retreat.

The U.S. troops and tanks occupying Hudong – who might have saved at least part of the task force – had been ordered back to Hagaru-ri the previous day (an action which remains controversial).

Here the Chinese renewed their attack, swarming among the trucks, throwing white phosphorus grenades into vehicles loaded with wounded, setting some of them on fire.

[10] The 27th Corps was later criticized by PLA historians for not making any serious attempts to gather POW's, thus enabling so many members of Task Force Faith to reach safety and fight again.

The so-called Provisional Battalion (known as "31/7" under Lieutenant Colonel Berry K. Anderson) was actually formed into two small battalions of three rifle companies each, 3/31 (Major Carl Witte) with I, K and L, 1/32 (Major Robert Jones) with companies A, B and C. During the night of 1 December, hundreds of survivors from the task force reached Marine positions south of the reservoir at Hagaru-ri.

Of the 2,500 troops trapped by the Chinese north of the roadblock, about 1,500 eventually made it back to American lines, the majority of them wounded or badly frostbitten.

Chinese documents and research by historians Marine Corps Major Parrot and Roy Appleman[citation needed] provided evidence that the RCT-31 had fought bravely and performed well given the circumstances.

[11][12] Of the 1,777 American soldiers of RCT-31 positioned at Chosin Reservoir from 27 Nov–2 Dec 1950, 1,392 were missing in action, either unrecovered killed or prisoners of war, by December 12.