During the Chosin Reservoir battle, why didn’t the Chinese obliterate the U.S. Marines and instead let them do a semi-orderly retreat?

Asked on Quora.

The Chinese did not allow the Marines’ an orderly retreat, they did everything in their power to annihilate them! Chinese sources say they had 450,000 casualties with 100,000 KIA while they fought UN forces in that war. But going back to the fight at the Chosin Reservoir.

“The engagement started when the American forces of the 1st Marine Division and the X Corps (who were pushing north in pursuit of the Chinese) saw themselves unexpectedly surrounded by an entire Chinese Army Group. Over the following two weeks, the Americans managed to break out of the Chinese encirclement and reach the coast where they were evacuated.” MacAuther was totally convinced that the Chinees would not enter the war and was also convinced that the War would be over by Christmas. He was wrong.

“On November 27th, the Chinese launched attacks against American forces moving through the road that lead to Koto-Ri. Caught by surprise, the American forces were surrounded and cut-off into several small pockets. The Marines desperately defended their positions against continual Chinese assaults but risking to be overrun, the Americans started retreating on December 6th, using air strikes to support their breakout from the Chinese blockade and escaping to the South. The objective of the retreat was the city of Hungnam where they arrived on December the 11th. Chosin Reservoir was a costly victory for the Chinese, costing them almost 50,000 casualties, while the Americans suffered 17,843 casualties.”

The battle was fought over some of the roughest terrain during some of the harshest winter weather conditions of the Korean War.[1]:24 The road was created by cutting through the hilly terrain of Korea, with steep climbs and drops. Dominant peaks, such as the Funchilin Pass and the Toktong Pass (40°23′38″N 127°09′40″E / 40.3938°N 127.161°E), overlook the entire length of the road. The road’s quality was poor, and in some places it was reduced to a one lane gravel trail.[1]:28–31 On 14 November 1950, a cold front from Siberia descended over the Chosin Reservoir, and the temperature plunged, according to estimates, to as low as −36 °F (−38 °C).[1]:xi The cold weather was accompanied by frozen ground, creating considerable danger of frostbite casualties, icy roads, and weapon malfunctions. Medical supplies froze; morphine syrettes had to be defrosted in a medic’s mouth before they could be injected; frozen blood plasma was useless on the battlefield. Even cutting off clothing to deal with a wound risked gangrene and frostbite. Batteries used for the Jeeps and radios did not function properly in the temperature and quickly ran down.[15] The lubrication in the guns gelled and rendered them useless in battle. Likewise, the springs on the firing pins would not strike hard enough to fire the round, or would jam.

Song Shilun (middle), commander of the People’s Volunteer Army 9th Army at Chosin Reservoir 

“Despite the loss of territory, the U.S. forces remained more intact and less ravaged than their Chinese counterparts. 17 Americans from 3 military branches received Medals of Honor for their valor in the engagements. The UN forces who served that day live on forever in military history as the ‘Chosin Few’. Many of the casualties were later exchanged to receive burials and honors between the UN and Communists, in what would become known as ‘Operation Glory’. Many of the unidentified bodies were buried at Honolulu’s Punchbowl Crater in the National Memorial Cemetery of the Pacific.”

Outcome:

The bulk of the PVA Ninth Army crossed the North Korean border on 10 November and arrived, undetected, around Chosin on 17 November. Chinese reconnaissance revealed a number of weaknesses in the UN dispositions. The two American garrisons on either side of the reservoir were unable to support each other, and it was clear that the road junction south of the reservoir at Hagaru-ri, – although strategically important – was only lightly defended. The Chinese were aware that the road running south of the reservoir to Koto-ri and on to the port of Hungnam appeared to be the Americans’ only line of retreat. The Chinese plan was to neutralize the three positions around the reservoir and then, as the UN forces came in from the south to relieve them, they in turn would be encircled and destroyed. The only difficulty the Chinese had was determining the actual strength of the UN forces since time was short. They nevertheless felt confident that their 60,000 men could overwhelm the relatively small detachments confronting them. Moreover, by infiltrating and maximizing the element of surprise they would be able to defeat the Westerners while suffering relatively low casualties. What the Chinese commanders did not realize was that the US 1st Marine Division (reinforced by the British 41 Royal Marines Commando, and two American infantry battalions) had arrived at Yudam-ni, which meant that the total strength of UN forces was close to 27,000.

The Chinese began their attacks at night on 27 November. Ambushes were conducted against mobile units, while massive infantry assaults swept on to the defended garrisons around the reservoir. At Yudam-ni, the Marines were soon surrounded, and tried to make sense of the confused situation while fighting along a hastily formed perimeter. On the eastern side of the reservoir, Regiment Combat Team 31 found itself similarly isolated and under attack from two divisions, the 80th and 81st. Further south, US Marines at Koto-ri were being attacked by another division. Taken by surprise, each formation was initially fighting for its survival.

“Marine Sgt. Johnny Johnson marched into deadly combat the first day he landed in Korea and it didn’t stop until he was sent home. He fought from the tip of South Korea all the way to the China border. His battles marked the map of war like the tiny flecks of dirt and sand still stuck under his skin from a Chinese grenade.

He landed in 1950—the year of the worst winter in Korea in 100 years, when temperatures in the north plunged to 40 below zero, and tanks, rifles, jeeps and canned rations were frozen by the “Manchurian Wind Tunnel.” Johnson still buys his shoes extra-large and wears two pairs of socks, even in summer, because his bones cannot forget the bitter, grinding cold.

He was among 8,000 1st Division Marines who fought one of the most valiant, historic battles in U.S. military history at the Chosin Reservoir. They were outnumbered by 100,000 Chinese who came out of the mountains and “poured over the hills like water,” he says.

The Marines scraped and clawed out shallow foxholes, reinforced by stacks of enemy dead. Morphine Syrettes froze solid and had to be thawed in the mouths of medics as men suffered and bled to death. The Marines fought their way out, taking their wounded and dead draped on Jeeps like bucks in deer season.

“Retreat, hell,” said Marine Gen. Oliver P. Smith, “we’re just attacking in a different direction.”

The Chosin Reservoir Campaign of the Korean War is the stuff of legend in the Marine Corps. During the pivotal 1950 battle, 15,000 U.S. soldiers and Marines, alongside another 15,000 UN soldiers, fought through a force of 120,000 Chinese soldiers to reach the sea some 78 miles away.

Commencing on November 26, Smith’s men endured extreme cold and severe weather. The next day, the 5th and 7th Marines attacked from their positions near Yudam-ni, on the west bank of the reservoir, with some success against the PLA forces in the area. Over the next three days the 1st Marine Division successfully defended their positions at Yudam-ni and Hagaru-ri against Chinese human wave assaults. On November 29, Smith contacted Colonel “Chesty” Puller, commanding the 1st Marine Regiment, at Koto-ri and asked him to assemble a task force to re-open the road from there to Hagaru-ri.

By the end of the battle, U.S. Marines suffered 836 dead and around 10,000 wounded. The Army had 2,000 dead and 1,000 wounded. The Chinese had the most catastrophic losses. Intelligence reported the Chinese as saying American forces could beat any Chinese effort, no matter the size.

Six Chinese divisions were completely wiped out. Of the ten that attacked, only one would ever see action again. Though the exact numbers are not clear, historians estimate Chinese losses anywhere from 30,000 to 80,000 killed. The numbers of Chinese wounded may never be known.

Does that sound like the Chinees were allowing the Marine’s semi-orderly retreat?