Five years of peace were spent at Camp Shanks, New York; Camp Swift, Texas; and Fort Lewis, Washington. With the entry of the United Nations into the Korean conflict and the commitment of the Second Infantry Division to the Korean peninsula, the 9th Infantry once again readied for war.
Manchu troops were the first element of the Indianhead Division to touch Korean soil when they arrived at the Korean port city of Pusan on 31 July 1950. The Manchus were immediately placed on line in defense of the Pusan Perimeter and it received its baptism of fire in the battle of the Naktong Bulge. Later they broke out from that defensive position, and began the attack Northward, when they assaulted and seized Cloverleaf and Obong-Ni Ridge on 1 August 1950. The Regiment remained there until 0 1 September when the last North Korean attempt to annihilate the Pusan Perimeter defenders shattered the Regiment, thereby causing them to retreat momentarily. The Regimental Commander, Colonel Hill, reorganized approximately 800 Manchus, and together with the 5th Marine Regiment, counterattacked and regained Cloverleaf and Obong-Ni Ridge.
The Manchu Regiment participated in the breakout from the Pusan perimeter and began the advance north with the rest of the Eighth Army towards the Yalu River. The soldiers thought that the war would be over and that they would be home for Christmas as they neared the end of their push northward. Those beliefs were crushed on 25 November 1950 though, when several Red Chinese Armies attacked the Eighth Army in the vicinity of the Chongehon River. The 9th Infantry Regiment was one of the hardest hit units and could only account for approximately one-half of its assigned members at daylight on 26 November. The 1st Battalion was overrun and the battalion commander, LTC Wolff was wounded in hand to hand combat with Chinese troops who overran them. He led a small group of soldiers out of the melee and they eventually linked up with other elements of the 9th Regiment. The heavy fighting continued for several days. The 1st Manchus were attached to the 23rd Infantry Regiment under the command of Colonel Paul Freeman. On 30 November 1950, the majority of the Manchu Regiment began to run the "Gauntlet" to Kunu-Ri with the rest of the 2nd Infantry Division. The 1st Battalion remained with the 23d Infantry Regiment to fight a rear guard action to cover the withdrawal of the rest of the 2nd Division. When Colonel Freeman received word that the Division was being annihilated running the gauntlet, he requested and received permission to withdraw along another route. He attempted to contact the 1st Manchus to order them to withdraw, but was unable to do so. Therefore, the remnants of the 1st Battalion, now under the command of Major Hinkley, were unable to comply with the withdrawal order, and the majority of those remaining battalion members are still carried as Missing In Action.
After running the gauntlet to Kunu-Ri, the remnants of the Regiment were withdrawn to an area south of the Korean capital of Seoul to refit. Manchus then spent the month of December 1950 on the monumental task of reorganizing, re-equipping, re-supplying and training, while patrolling the roads east of Seoul to Hongchon, Hoengsong and Wonju. Early January 1951 found the 9th patrolling to the northeast and northwest from defensive positions in Wonju, many times encountering enemy groups attempting to enter Wonju. The push northward by the Manchu Regiment began in early February l951,and continued until-near the middle of 1951,when they became involved in the bloody fighting that occurred along the present DMZ. In late July 1951 the Manchu Regiment participated in the capture of Hill II 79 (Taeu-San), one of the highest peaks in that area. In late August, the Manchus, under the command of LTC Gaylord M. Bishop, led the assault on the three hill mass (773, 940 and 983) which later became known as "Bloody Ridge." At the time of its capture on 5 September 1951, there were only two officers left in the three rifle companies of the 1st Battalion of the 9th Infantry Regiment.
On 18 September 1951 the Regiment was ordered to attack the ridge lines southwest of Heartbreak Ridge in an attempt to relieve pressure on the 23rd Infantry Regiment, which was attacking up the east-west spur of the ridge. After heavy fighting the Manchus secured their objective on 23 September. The North Koreans did not relinquish Heartbreak Ridge and in late September the Manchus were ordered to attack the west-side of the Mundung-Ni Valley in a final attempt to capture the ridge. The attack was successful and Heartbreak Ridge fell on 13 October 195 1.
The Regiment also participated in an engagement at Old Baldy, and on 28 December 1952 the Manchus were relieved from Pork Chop Hill and Old Baldy. On 29 January 1953 they returned to the front in the Little Gibraltar sector and conducted extensive patrolling. Special Ranger platoons, previously developed and used by each battalion while in the T-Bone battles, bore the brunt of this duty. After leaving Little Gibraltar, the Regiment moved to the sector of the line known as the Boomerang. It was located in that sector during the signing of the cease-fire pact on 27 July 1953. While the cease-fire negotiations were going on, however, a mass attack was executed by the Chinese forces on 18 July 1953, but they were again repulsed. The Regiment earned an additional Presidential Unit Citation for its gallant service in Hongchon, and the Manchus received streamers for the following campaigns while serving in Korea: UN Defensive, UN Offensive, CCF Intervention, First UN Counteroffensive, CCF Spring Offensive, UN Summer-Fall Offensive, Second Korean Winter, Korea Summer-Fall 1952 Third Korean Winter Korea, Summer 1953.