Battle of Onjong The Battle of Onjong ( ) , also known as the Battle of Wenjing ( ) , was one of the first engagements between Chinese and United Nations forces during the Korean War . It took place around Onjong in present - day North Korea from October 25 to October 29 , 1950 . As the main focus of the Chinese First Phase Campaign , the Chinese 40th Corps conducted a series of ambushes against the Republic of Korea II Corps , effectively destroying the right flank of the United States Eighth Army while stopping the UN advances north toward the Yalu River . Background . The Korean War began in June 1950 with the Korean People ' s Army ( KPA ) of the north attacking the Republic of Korea in the south . The invasion was almost successful in conquering all of the Republic of Korea until the United Nations ( UN ) intervened , sending ground forces into the country under the command of the United States . The UN forces initially experienced early defeats until the Battle of the Pusan Perimeter , where the UN forces reversed North Korea ' s momentum . By October 1950 , the KPA was effectively destroyed by the UN forces after the landing at Inchon . Despite the strong objections from the People ' s Republic of China on North Korea ' s northern border , the US Eighth Army crossed the 38th parallel and advanced towards the Sino - Korean border at the Yalu River . As part of the Thanksgiving Offensive to end the war , the Republic of Korea ( ROK ) II Corps , which was composed of the ROK 6th , 7th and 8th Infantry Division , was ordered to attack north towards the Yalu River through the village of Onjong on October 23 , 1950 . In response to the UN advances , China ' s Chairman , Mao Zedong , ordered the People ' s Liberation Army ' s North East Frontier Force to enter North Korea and engage UN forces under the name People ' s Volunteer Army ( PVA ) . 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 the ROK II Corps , the vanguard and the right flank of the US Eighth Army , advancing up the along the Taebaek Mountains in the middle of the peninsula . After the Chinese leadership finally settled the issue of armed intervention on October 18 , Mao ordered the PVA to enter Korea on October 19 under strict secrecy . Prelude . Locations and terrain . Onjong is a crossroad village located at the lower Ch ' ongch ' on River Valley , northeast of Unsan . At the east of Onjong stands the town of Huich ' on , the staging area of the ROK II Corps for the Thanksgiving Offensive . To the north , Onjong is linked to the town of Kojang , which is located at away from the Yalu River . Because of the hilly terrain at the Sino - Korean Border , Onjong is one of the few access points into the Yalu River area . The terrain also limits troop movements while providing ideal grounds for ambushes . Forces and strategy . On October 24 , the ROK 6th Infantry Division of the ROK II Corps advanced westward from Huich ' on , and Onjong was captured on the same day . From Onjong , the ROK 7th Infantry Regiment of the ROK 6th Infantry Division turned north and advanced towards Kojang , while the ROK 2nd Infantry Regiment of the ROK 6th Infantry Division planned to advance northwest from Onjong towards Pukchin . Because the UN Command expected no opposition from the destroyed KPA , the advances were not coordinated between the UN units . As a result , the ROK 7th Infantry Regiment managed to wander into Chinese territory without much opposition , completely oblivious to the new threats surrounding them . While the Koreans were advancing towards the Yalu River , the Chinese were also trying to deploy their units for the upcoming First Phase Campaign . As the PVA Commander Peng Dehuai scrambled to set up his new command post at Taeyudong , the planned advance by the ROK 2nd Infantry Regiment threatened to overrun his position . Without any KPA units nearby to hide the presence of the Chinese , Peng was forced to start the First Phase Campaign early by moving the PVA 40th Corps to intercept the ROK 2nd Infantry Regiment near Onjong . On the night of October 24 , the 118th Division of the 40th Corps arrived at its designated blocking position . Meanwhile , the Chinese had set up numerous ambush positions on the ridges overlooking the Onjong - Pukchin road . Battle . Initial contacts . On the morning of October 25 and with its 3rd Battalion on point , the ROK 2nd Infantry Regiment started to advance northwest towards Pukchin . The Koreans soon came under fire to the west of Onjong . The 3rd Battalion dismounted from their vehicles to disperse what they thought would be a small force of KPA , but the two Chinese regiments on the high ground immediately began pouring heavy fire onto the Korean left , front and right flanks . The 3rd Battalion broke instantly , abandoning most of its vehicles and artillery along the way . About 400 survivors managed to escape the trap and fall back into Onjong . When the ROK 2nd Infantry Regiment learned that the 3rd Battalion was under heavy attack , its 2nd Battalion was moved forward to support the 3rd Battalion while its 1st Battalion was sent back to Onjong . Although the 2nd Battalion was turned back after encountering strong resistances , the South Koreans managed to capture several Chinese prisoners who revealed that there were nearly 10 , 000 Chinese soldiers waiting down the road . At the same time , the PVA High Command ordered the PVA 120th Division of the 40th Corps to join the battle while the rest of the 40th Corps was busy setting up roadblocks around Onjong . With all the roadblocks in place by midnight , the PVA 118th Division and one regiment from the PVA 120th Division attacked Onjong on October 26 at 0330 , and the ROK 2nd Infantry Regiment was dispersed within 30 minutes . Although Colonel Ham Byung Sun , commander of the ROK 2nd Infantry Regiment , managed to rally his troops east of Onjong , the Chinese were still able to penetrate the new position within an hour . At this point not a single company of the regiment was left intact , and the ROK 2nd Infantry Regiment ceased to be an organized unit . Approximately 2 , 700 men of the 3 , 100 in the regiment eventually escaped to the Ch ' ongch ' on River . The 3rd Battalion ' s Korean Military Advisory Group ( KMAG ) adviser , Lieutenant Glen C . Jones , was among those captured , and he eventually died in a North Korean prison camp . Captain Paul V . S . Liles of the KMAG also fell captive to the Chinese . Second ambush . The loss of surprise due to the early start of the First Phase Campaign greatly disappointed Mao . Nevertheless , Mao still urged Peng to destroy the South Koreans by baiting them with trapped ROK units . At the same time , Major General Yu Jai Hung , commander of the ROK II Corps , sent the ROK 19th Infantry Regiment of the ROK 6th Infantry Division and the ROK 10th Infantry Regiment of the ROK 8th Infantry Division to recapture Onjong and to salvage the lost equipment from the battle . The ROK 7th Infantry Regiment was also ordered to retreat south with the ROK 6th Infantry Division . Hoping to draw the rest of the ROK II Corps into the open , Peng ordered the PVA 118th Division to swing north and to trap the retreating ROK 7th Infantry Regiment , while the PVA 119th and the 120th Division of the 40th Corps would wait to ambush any rescue forces passing through Onjong . On October 27 , the PVA 118th Division isolated the ROK 7th Infantry Regiment by cutting the road between Kojang and Onjong , but the ROK 7th Infantry Regiment did not reach the roadblock due to the lack of fuel . Upon realizing that the ROK II Corps had not fallen for the deception , Peng ordered the 119th and the 120th Divisions to destroy the ROK 10th and 19th Infantry Regiment . On the night of October 28 , the ambush by the two Chinese divisions quickly decimated the advancing ROK regiments at the east of Onjong , and the Chinese roadblocks in the rear areas forced the South Korean soldiers to abandon all vehicles and artillery in order to escape . The ROK 7th Infantry Regiment had now become the only surviving formation of the ROK 6th Infantry Division , but it too was ambushed by the PVA 118th Division on October 29 south of Kojang . The PVA 118th Division was ordered to wait for reinforcements from the 50th Corps , but the 118th Division attacked alone on the night of October 29 to prevent the Koreans from escaping . After a two hour battle , the ROK 7th Infantry Regiment was forced to disperse with its survivors scattered into the hills . About 875 officers and 3 , 552 other soldiers managed to escape , while Major Harry Fleming of the KMAG was wounded in 15 places and was later captured by the Chinese . Aftermath . With the loss of the ROK 6th Infantry Division and the ROK 10th Infantry Regiment from the ROK 8th Infantry Division , the ROK II Corps was decimated , and effectively ceased to be an organized fighting force . This meant the right flank of the US Eighth Army was completely open to the Chinese forces , which were now advancing south to overwhelm the UN forces . Exploiting the situation , the Chinese launched another attack on the now exposed Eighth Army center , resulting in the loss of the ROK 15th Infantry Regiment and the US 8th Cavalry Regiment at the Battle of Unsan . With the Chinese forces pouring into the rear of the UN lines , the Eighth Army was forced to retreat to the Ch ' ongch ' on River . Only the stubborn defense of Kunu - ri by the US 5th Regimental Combat Team and the ROK 7th Infantry Division on November 4 managed to stop the Chinese advance and prevented a disastrous defeat for the Eighth Army . By November 5 , logistics difficulties forced the Chinese to end the First Phase Campaign . Although the Chinese were unable to exploit the breakthrough in the UN lines , the weakness of the ROK II Corps on the Eighth Army ' s right flank was exposed to the Chinese commanders . During the planning of the Chinese Second Phase Campaign , Peng would again focus his attention towards the ROK II Corps at the Eighth Army ' s right flank , resulting in a disastrous defeat for the UN forces at the Battle of the Ch ' ongch ' on River . To commemorate this battle as China ' s official entry into the Korean War , October 25 is currently the War to Resist America and Aid Korea Memorial Day in China .