X Corps ( United States ) X Corps was a corps of the United States Army in World War II and the Korean War . World War II . The X Corps was activated in May 1942 at Sherman , Texas . It embarked for the Pacific Theater in July 1944 after two changes of station and participation in maneuvers in Louisiana and at the California - Arizona maneuver area . X Corps took part in the following campaigns : New Guinea , Leyte , and Southern Philippines . As part of the Sixth Army , X Corps took part in the Philippines campaign of 1944 – 45 , beginning with the invasion of Leyte . For its involvement , the X Corps received the Philippine Presidential Unit Citation with a streamer embroidered 17 October 1944 – 4 July 1945 . X Corps became inactive in 1946 . Korean War . Operation CHROMITE . The Battle of Inchon During the Korean War , it took part in Operation Chromite , the landings at Inchon , where it had the 1st Marine Division , the 7th Infantry Division and other US Army units under its command . The embryonic planning group for CHROMITE originally was known to insiders as " Force X " and the entire scheme was cloaked in absolute secrecy ; to outsiders the small planning staff was known only as the Special Planning Staff of general headquarters , Far East Command . As the organization grew , due to bureaucratic entanglements supply orders were rejected because " Force X " was not referenced as a proper organization anywhere in Army manuals . General of the Army Douglas MacArthur ( Supreme Commander Allied Powers ) asked his Chief of Staff , Major General Ned Almond , to suggest a new name . Force X ' s Roman numeral ten reminded Almond of a corps which had fought under MacArthur in the last war — " why not call it the X Corps ? " he asked . MacArthur was delighted and approved of the name . General Almond was subsequently chosen by MacArthur as X Corps ' new commander . The Marines first captured an island offshore of Inchon as a prelude to the assault and at the next tide , the main attack went in . Despite the noise of the attack on the offshore island , it completely surprised the North Korean forces . The Marines then moved on to the capital city of Seoul ; in heavy fighting they eventually drove out the North Korean defenders . The US Army ' s 7th Infantry Division , which had landed later at Inchon , engaged the enemy on the outskirts of Seoul , destroying an armored regiment . Inchon had a very large tidal range , and was thus very risky to use as a landing site . Nonetheless , the landing proved to be an enormous success . It is by far the largest amphibious assault to have taken place since World War II , and one of the boldest . Operation TAILBOARD . The X Corps ' planned amphibious landing on the east coast of North Korea is amended by UNC OPORD No . 4 culminating in a withdrawal to the sea . The Battle of Chosin Reservoir After the landing at Inchon , X Corps attacked up the Korean peninsula on the left flank of Eighth Army . However , it was withdrawn to prepare for another amphibious assault , this time at Wonsan on the eastern coast . This action proved to be a mistake on two counts . First , forces of the Eighth Army moving by land reached Wonsan before the assault went in . Second , it proved to be too far for UN forces to go . After an administrative landing at Wonsan , X Corps , now including the US 3d Infantry Division , advanced inland northwest towards the Yalu River with the First Republic of Korea ( I ROK ) Corps made up of two ROK Divisions in the far north or right flank . The US 7th Infantry Division was in the center and the US 1st Marine Division ( MARDIV ) on the southern or left flank of the X Corps attack . 3d Infantry Division was initially in reserve . As elements of the I ROK Corps and 7th Infantry Division closed on the Manchurian border , the 1st Marine Division hesitated and became bogged down in the vicinity of the Chosin Reservoir ( Changjin Ho ) . The Chinese Communist Forces choose this moment to intervene " en masse " in the war . They crossed the Yalu into northern Korea and engaged 8th Army and X Corps across their frontages . The Marines were on both left and right sides of the Changjin reservoir . Regimental Combat Team 31 ( RCT31 AKA Task Force Faith ) of the Army ' s 7th Infantry Division replaced the 5th Marine Regiment on the east side of the reservoir in a piecemeal fashion with only two of its maneuver battalions in place before heavy engagement with the enemy commenced . X Corps was strung out along many miles in sub - freezing temperatures with the ROK troops and the 7th Infantry Division to the north in contact with enemy forces . Regimental Combat Team 31 was too far from its parent Division for support and without organic tank support and its third maneuver element ; it was decimated by the onslaught of the Chinese . The 1st MARDIV fared better and with remnants of RCT31 , Army Engineers and X Corps support personnel , began its move to the sea moving through elements of the 3rd Infantry Division ( Task Force Dog from the 7th Infantry Regiment , and a reinforced battalion of the 65th Infantry Regiment ) who provided flank and rear guard cover for the withdrawing units . The 7th Infantry Division in the center and the I ROK Corps on the right flank also began withdrawing to the Hungnam beachhead . The Marines withdrew through the 3d Infantry Division with intermittent contact with Chinese forces up to Sudong . The extreme temperatures during this period caused the majority of the casualties for X Corps . The Marines managed to reach the safety of Hungnam first , where the 3rd and 7th Infantry Divisions and I ROK Corps provided perimeter defense . The Marines were evacuated by the middle of December , followed by the 7th Infantry Division , I ROK Corps and the last of the X Corps ' elements . The 3d Infantry Division was last to leave the beach and evacuated on 24 December 1950 . For intrepid service during the Battle of the Chosin Reservoir with Chinese Communist Forces : U . S . Army Lieutenant Colonel Don C . Faith , Jr . , having assumed command of Regimental Combat Team 31 7th Infantry Division , for actions during the period 27 November through 1 December 1950 , U . S . Army Lieutenant Colonel John U . D . Page , of the X Corps Artillery , having distinguished himself in action during the period of 29 November to 10 December 1950 and U . S . Marine Corps Staff Sergeant William G . Windrich , Company I , 3d Battalion , 5th Marines , 1 December 1950 were posthumously awarded the Medal of Honor . Receiving the Medal of Honor in person : U . S . Marine Corps Lieutenant Colonel Ray Davis , in command of the 1st Battalion 7th Marines for his actions 1 through 4 December 1950 , U . S . Marine Corps Captain William E . Barber , in command of Fox Company 2nd Battalion 7th Marines , for his actions during the period 28 November through 2 December 1950 , U . S . Marine Corps Staff Sergeant Robert Kennemore , Company E , 2d Battalion , 7th Marines , for his actions during the period 27 and 28 November 1950 , and U . S . Marine Corps Private First Class Hector A . Cafferata , Jr . , Company F , 2d Battalion , 7th Marines , for his actions on 28 November 1950 . Later actions . After the withdrawal from the northeast coast , and once its units had been reconstituted , X Corps went into the line , and remained there for the rest of the war . It is widely contended that X Corps remained outside of the direct command of Eighth Army too long . X Corps reporting directly to the Supreme Commander had been necessary for the Inchon landings and still defensible for the Wonsan attack . However , after it entered the main line , conventional military doctrine indicated that it should have been placed immediately under the command of Eighth Army . General Douglas MacArthur , the commander of the United States forces , was accused of favoritism towards Edward Almond , the controversial commander of X Corps , who was dual - hatted as the commander of X Corps and MacArthur ' s Chief of Staff and his personal friend . After X Corps was placed under the command of Eighth Army , it performed with powerful strength for the rest of the war . Post - Korean War . In the years following the Korean War , X Corps served as a regional headquarters , having administrative , logistical , and training responsibility for both active and Army Reserve units in the northwestern portion of the Continental United States . X Corps was deactivated on 31 March 1968 , as part of the compromise between U . S . Secretary of Defense Robert S . McNamara who wanted to merge the Army Reserve into the Army National Guard , and the United States Congress who wanted to maintain the Army Reserve as it then existed . Under the compromise plan , all of the combat divisions and most separate combat brigades of the Army Reserve were deactivated with a corresponding increase in the National Guard ; at the same time , non - divisional combat support and combat service support units were reallocated in the Army Reserve . The fourteen area corps were deactivated ; in their place , eighteen army reserve commands ( " ARCOMs " ) were established . Each ARCOM was , in turn , assigned to one of five continental U . S . armies ( " CONUSAs " ) under Continental Army Command ( " CONARC " ) . The bulk of X Corps ' Army Reserve units were assigned to the 124th Army Reserve Command .