IX Corps ( United States ) IX Corps was a corps of the United States Army . For most of its operational history , IX Corps was headquartered in or around Japan and subordinate to US Army commands in the Far East . Created following World War I , the corps was not activated for use until just before World War II almost 20 years later . The corps spent most of World War II in charge of defenses on the West Coast of the United States , before moving to Hawaii and Leyte to plan and organize operations for US forces advancing across the Pacific . Following the end of the war , IX Corps participated in the occupation of mainland Japan . The corps ' only combat came in the Korean War . It is best known for its exploits as a senior command of the Eighth United States Army , commanding front line UN forces in numerous offensives and counteroffensives throughout the war . The corps served on the front lines for most of the conflict and took command of several combat divisions at a time . Following the end of the Korean War , IX Corps remained in Korea for several years until it was moved to Japan . The corps spent almost 40 years as an administrative command of the US Army forces there , overseeing administrative functions but no combat . It was finally deactivated and consolidated in 1994 . History . The IX Corps headquarters was first constituted on 29 July 1921 in the organized reserves , a new corps formation intended to compliment the existing corps commands in the active duty component of the force by providing command to reserve units . It was assigned a shoulder sleeve insignia shortly thereafter . Though the corps was not activated , it remained on the organizational rolls of the Army , to be called on when needed . On 1 October 1933 , the corps was moved to the active duty roster , though it remained deactivated . World War II . The corps headquarters was finally activated on 24 October 1940 at Fort Lewis , Washington as part of a large buildup of the US Army in response to conflicts around the world . It immediately began training of combat units in preparation for deployment . One year later , IX Corps took command of the Camp Murray staging area in Washington , responsible for training Army National Guard forces in addition to its responsibilities training active duty and reserve units . Following the Japanese attack on Pearl Harbor in late 1941 , IX Corps was assigned to defensive duties on the West Coast of the United States , specifically the central and northern regions of the coast . The corps oversaw defenses on the West Coast for the majority of the war , but in 1944 it was moved to Fort McPherson , Georgia in preparation for deployment overseas . Planning . The corps trained at Fort McPherson in preparation for deployment to the Pacific Theater of Operations . On 25 September 1944 , the corps closed headquarters at Fort McPherson and moved to Hawaii . When it arrived in Hawaii , IX Corps was put under the command of the Tenth United States Army . Under the Tenth Army , IX Corps was assigned two missions . In 1944 , it was primarily concerned with formulating plans for an invasion of the coastal regions of Japanese - held China . Later in 1944 and early 1945 , it was placed in charge of preparing the rest of the Tenth Army for movement to Okinawa in preparation for an invasion of the island , which was launched in April 1945 . When General of the Army Douglas MacArthur took overall command of Pacific Forces , IX Corps was moved to Leyte in the Philippine Islands and was assigned to the Sixth United States Army in July 1945 . In Leyte , the corps was tasked with the planning of Operation Downfall , the invasion of mainland Japan , specifically the island of Kyushu . It was also tasked with planning occupation once Japan surrendered . IX Corps was assigned as one of four Corps under the command of the Sixth Army , with a strength of 14 divisions . With the 77th Infantry Division , the 81st Infantry Division and 98th Infantry Division , a force of 79 , 000 men , IX Corps would serve as the Sixth Army ' s reserve force during the initial invasion . Before the assault could be launched , Japan surrendered in August 1945 , following the use of nuclear weapons on Hiroshima and Nagasaki . Occupation . Following the surrender , IX Corps was assigned command of occupation forces on the northern island of Hokkaidō . IX Corps transferred its headquarters in October 1945 to Sapporo for occupation duties . The next few years were a period during which the terms of the surrender were supervised and enforced ; Japanese military installations and material were seized , troops were disarmed and discharged , and weapons of warfare disposed of . The duties of the occupation force included conversion of industry , repatriation of foreign nationals , and supervision of the complex features of all phases of Japanese government , economics , education , and industry . As the occupation duties were accomplished , the occupation force continued to downsize as more troops returned home and their units were deactivated . By 1950 , the Sixth Army had left Japan , and the occupation force was reduced to the Eighth United States Army commanding two corps and four under - strength divisions ; the I Corps , commanding the 24th Infantry Division and 25th Infantry Division , and the IX Corps , commanding the 1st Cavalry Division and the 7th Infantry Division . IX Corps had been moved to Sendai as the occupation forces shifted as a result of the downsizing . As part of further downsizing , IX Corps was deactivated on 28 March 1950 , and its command responsibilities were consolidated with other units . Korean War . Only a few months later , the Korean War began , and units from Japan began streaming into South Korea . The Eighth Army , taking charge of the conflict , requested the activation of three corps headquarters for its growing command of UN forces . IX Corps was activated on 10 August 1950 at Fort Sheridan , Illinois . Most of its personnel were transferred from the headquarters of the Fifth United States Army . Pusan Perimeter . IX Corps arrived at the Pusan Perimeter in Korea on 22 September 1950 , and became operational the next day when it took command of the 2nd Infantry Division and 25th Infantry Division . It took charge of the western flank of the perimeter , defending the Naktong River area against attacking North Korean units . Amphibious landings at Inchon by X Corps hit North Korean forces from behind , allowing I Corps and IX Corps to break out of Pusan , I Corps to the north and IX Corps to the south . Four days later I Corps troops pushed northward against crumbling enemy opposition to establish contact with forces of the 7th Infantry Division driving southward from the beachhead . Major elements of the North Korean Army were destroyed and cut off in this aggressive penetration ; the link - up was effected south of Suwon on 26 September . The offensive was continued northwards , past Seoul , and across the 38th Parallel on 1 October . The momentum of the attack was maintained , and the race to the North Korean capitol , Pyongyang , ended on 19 October when elements of the South Korean 1st Infantry Division and US 1st Cavalry Division both entered the city . The advance continued , but against unexpectedly stiffening enemy resistance . On 25 October the first Chinese prisoners on the Eighth Army front were taken by I Corps troops . By the end of October the city of Chongju , forty miles from the Yalu River border of North Korea , had been captured . IX Corps advanced in the center of the Army , with I Corps along the west coast and X Corps operating independently further east . Commanders hoped the offensive would end the war " by Christmas . " Chinese intervention . On 27 November , China entered the war on the side of North Korea against the UN . Massed Chinese attacks were immediately launched against troops of the corps , with Chinese forces penetrating the corps ' rear from its exposed east flank . The 2nd Infantry Division , at the front of IX Corp ' s advance in Kunuri , was overwhelmed from all sides by Chinese forces of the 40th CPV Army Corps , and elements from the 38th CPV Army Corps on 29 November in the Battle of Kunuri . By 1 December , the division was almost completely destroyed ; it lost virtually all of its heavy equipment and vehicles , as well as suffering 4 , 940 men killed or missing . The 25th Infantry Division , on its western flank , was also hit by overwhelming Chinese forces of the 39th CPV Army Corps , facing strong attacks and suffering heavy casualties and losses in equipment in the Battle of Ch ' ongch ' on River . However , it was spared the same losses as the 2nd Infantry Division by escaping across the Ch ' ongch ' on River . The Eighth Army suffered heavy casualties , ordering a complete withdraw to the Imjin River , south of the 38th parallel , having been devastated by the overwhelming Chinese force . IX Corps retreated along the western coast to safety via Anju . In the wake of the retreat , the disorganized Eighth Army regrouped and re - formed . The 2nd and 25th Infantry Divisions had suffered so many losses that both divisions were designated combat ineffective , and were relegated to the Eighth Army ' s reserve to rebuild . IX Corps was then assigned the 1st Cavalry Division , 24th Infantry Division , 1st Marine Division and South Korean 6th Infantry Division , as well as the 187th Airborne Regimental Combat Team . The corps ' American forces were also reinforced at this point with battalions from Greece and the Philippines , as well as the 27th Commonwealth Brigade . On 1 January 1951 , 500 , 000 Chinese troops attacked the Eighth Army ' s line at the Imjin River , forcing them back 50 miles and allowing the Chinese to capture Seoul . The Chinese eventually advanced too far for their supply lines to adequately support them , and their attack stalled . The Eighth Army , battered by the Chinese assault , began to prepare spring offensives to retake lost ground and keep the retreating Chinese forces from being able to rest . Following the establishment of defenses south of the capital city , General Matthew B . Ridgway ordered I , IX , and X Corps to conduct a general counteroffensive against the Chinese forces on 25 January , Operation Thunderbolt . The three corps advanced north with IX Corps at the center of the line , on both sides of the Han River . The corps were to advance steadily northward , protected by heavy artillery and close air support , until they captured Seoul . IX Corps was tasked with capturing Chipyong - ni , southeast of Seoul while providing support to the other two corps . However , it encountered stiff resistance from Chinese forces dug into the hilly country around Chipyong - ni and was still bogged down in combat by 2 February . Chinese forces had established machine gun nests in the hillside and mined roads to slow the corps ' advance . In response , X Corps launched Operation Roundup , hoping to take pressure off of IX Corps and to force the Chinese to abandon Seoul . Between February and March , the corps participated in Operation Killer , pushing Chinese forces north of the Han River . This operation was quickly followed up with Operation Ripper , which retook Seoul in March . After this , Operations Rugged and Dauntless in April saw Eighth Army forces advance north of the 38th parallel and reestablish themselves along the Kansas Line and Utah Line , respectively . In March , the 187th Airborne Regimental Combat Team and the 1st Marine Division were reassigned , and the corps was given command of the 7th Infantry Division and the South Korean 2nd Infantry Division in their place . In late April , the Chinese launched a major counterattack . 486 , 000 Chinese troops assaulted I Corps and IX Corps ' sector of the lines . Most of the UN forces were able to hold their ground , but the Chinese broke through at Kapyong , where the South Korean 6th Division was destroyed by the 13th CPV Army Corps , which penetrated the line and threatened to encircle the American divisions to the west . The 1st Marine Division and 27th British Commonwealth Brigade were able to drive the 13th Army Corps back while the 24th and 25th Divisions withdrew on 25 April . The line was pushed back to Seoul but managed to hold . A second offensive the next month was similarly unsuccessful , as Chinese and North Korean forces suffered heavy casualties but were unable to push back the Eighth Army forces . The I and IX Corps had blunted the offensive at the No Name Line , just north of Seoul . Stalemate . In September , the UN Forces launched another counteroffensive with the 24th Infantry Division at the center of the line , west of the Hwachon Reservoir . Three of I Corps divisions advanced behind the 24th Infantry Division in Operation Commando . Flanked by the South Korean 2nd and 6th Divisions , the 24th advanced past Kumwha , engaging the 20th and 27th CPV Armies . These attacks were fierce , though enemy resistance was not as strong as it had been in previous offensives . In November , the Chinese attempted to counter this attack , but were unsuccessful . It was at this point , after several successive counteroffensives that saw both sides fighting intensely over the same ground , that the two sides started serious peace negotiations . In January 1952 , IX Corps was again reorganized , now containing the 7th Infantry Division and the newly arrived 45th Infantry Division . Two months later , it was reorganized with the 2nd Infantry Division , the 40th Infantry Division , and the South Korean 2nd , 3rd , and Capital Divisions . In October 1952 , Chinese forces conducted a large offensive against IX Corps ' sector , against the hilly countryside around the Iron Triangle region of Chorwon , Kumhwa , and Pyongyang . The 38th CPV Field Army sent heavy assaults against the South Korean forces guarding Hill 395 in the Battle of White Horse . At the same time , Chinese forces attacked Arrowhead Hill , which was held by the 2nd Infantry Division two miles away . Both hills changed hands several times , but after two weeks and almost 10 , 000 casualties , the Chinese were unsuccessful in capturing either objective and withdrew . On 14 October 1952 , IX Corps launched an offensive , Operation Showdown , intended to improve its defensive lines by capturing a complex of hills and force Chinese lines back . This complex included Pike ' s Peak , Jane Russell Hill , Sandy Hill , and Triangle Hill , northeast of Kumhwa . The 7th Infantry Division advanced , encountering resistance from the 15th Chinese Field Army . In the ensuing Battle of Triangle Hill , the four hills were captured and recaptured by both sides several times in the heaviest fighting that year . Eventually , the UN forces withdrew having been unsuccessful in capturing their objectives . UN forces suffered 9 , 000 killed and the Chinese suffered 19 , 000 killed or wounded during the fighting . The result of the battle had only been a slight improvement in IX Corps ' positions , as Chinese positions had been too well fortified for the UN forces to take and hold the ground . For the remainder of the year , US and Chinese forces both conducted a series of smaller raids on each other ' s lines , avoiding major conflicts , as armistice negotiations continued unsuccessfully . In November , the Chinese launched another offensive to retake ground lost during these operations , which was again repulsed by UN forces . In January 1953 , IX Corps was reorganized for the last time and now consisted entirely of South Korean forces . It retained command of the South Korean 3rd Infantry Division and Capital Division , and gained command of the South Korean 9th Infantry Division . The corps maintained a position around Chorwon , flanked to the west by I Corps and to the east by the South Korean II Corps . Though the South Korean II Corps saw a major attack against its lines in July 1953 , IX Corps and its divisions only fought in limited engagements , usually with company - sized formations attacking or defending fortified positions against the Chinese until the end of the war . No major attacks against the corps were conducted through 1953 , until the armistice was signed in July , ending the war . After Korea . Following the armistice , IX Corps remained on the front lines in Korea in case hostilities erupted again . On 1 January 1954 , it was reassigned from the Eighth Army to the Far East United States Army Forces . Camp Sendai was Headquarters XVI and then IX Corps during the 1950s . In November 1956 , over three years after the signing of the armistice , IX Corps headquarters left the front lines , moving to Fort Buckner , Okinawa , and the divisions under its command were shifted to the command of other headquarters . There , as a part of consolidation of US forces in the region , IX Corps merged with the US Army ' s Ryukyus command to form a joint command element on 1 January 1957 . The command oversaw administrative duties of US forces in the Ryukyu Islands area . On February 2 , 1956 , IX Corps moved from mainland Japan to Fort Buckner , Okinawa , where it merged with Headquarters Ryukyus Command , to form HQ RYCOM / IX Corps on January 1 , 1957 . ( Globalsecurity . org ) The Army had previously in the late 1940s formed Ryukyu Command from the previous Okinawa Base Command . In 1961 , part of the IX Corps was split into the 9th Regional Support Command , subordinate to the US Army Pacific command . Though the 9th Regional Support Command was an independent unit , it continued to operate closely with IX Corps . It received a distinctive unit insignia in 1969 . In 1972 , following further consolidation of US forces in the area , the US Army command on the Ryukyus was disbanded , and IX Corps merged with United States Army Japan to form a consolidated command of all US forces in the western Pacific region . There , its responsibilities included administrative oversight of US forces as well as conducting training and exercises with US and other units in the region . A major change in the Army ' s command and organizational structure in the Pacific occurred on May 15 , 1972 , in conjunction with the return of Okinawa to Japanese control after twenty - seven years of administration by the United States . Under the complex reorganization that accompanied reversion , Headquarters , IX U . S . Army Corps , was transferred from Okinawa and collocated with Headquarters , U . S . Army Japan , to form Headquarters , U . S . Army , Japan / IX Corps , at Camp Zama , Japan . On Okinawa , Headquarters , U . S . Army , Ryukyu Islands , and Headquarters , 2d Logistical Command , were inactivated and a U . S . Army Base Command , Okinawa , was established to command and support all Army units there and perform the theater logistic functions for United States and allied forces in the Pacific . For the next 20 years , IX Corps remained in the region conducting training and oversight to US Army forces in the area , and as such it was never deployed to support any other US Army contingencies . IX Corps remained a command component of United States Army Japan until 1994 , when it was deactivated . At this point , the lineage of the corps was assumed by the 9th Theater Army Area Command , which was activated in its place . Lieutenant General James E . Moore was : Lieutenant General Donald P . Booth was : Lt . Gen . Albert Watson , II was : Lt . Gen . Ferdinand T . Unger was : U . S . Army Ryukyu Islands ( USARYIS ) was active at lest until from 22 April 1969 – 21 October 1970 . Honors . The IX Corps was awarded one campaign streamer for service in World War II , and nine campaign streamers and two unit decorations during its service in the Korean War for a total of ten streamers and two unit decorations in its operational history .