U.S. I Corps

I Corps is a corps of the United States Army headquartered in Joint Base Lewis-McChord, Washington. It is a major formation of United States Army Pacific (USARPAC) and its current mission involves administrative oversight of Army units in the Asia-Pacific region, including the Pacific Pathways program.

Activated in World War I in France, I Corps oversaw US Army divisions as they repelled several major German offensives and advanced into Germany. The corps was deactivated following the end of the war. Reactivated for service in World War II, the corps took command of divisions in the south Pacific, leading US and Australian Army forces as they pushed the Japanese army out of New Guinea. It went on to be one of the principal leading elements in the Battle of Luzon, liberating the Philippines. It then took charge as one of the administrative headquarters in the occupation of Japan.

Deployed to Korea at the start of the Korean War, the corps was one of three corps that remained in the country for the entire US participation in the conflict, commanding US, British, and South Korean forces through three years of back-and-forth campaigns against North Korean and Chinese forces. Following the end of the war, it remained in Korea for almost 20 years guarding the Korean Demilitarized Zone. Active today, the corps acts as a subordinate headquarters of United States Army Pacific, and has also seen deployments in support of Operation Iraqi Freedom and Operation Enduring Freedom.

History

World War I

Following the American declaration of war on Germany, on 6 April 1917, I Corps was organized and activated on 15–20 January 1918, in the National Army in Neufchâteau, France, the first of several corps-sized formations intended to command divisions of the American Expeditionary Force in Europe during World War I. Assisted by the French XXXII Corps, the headquarters was organized and trained; on 20 January, Major General Hunter Liggett took command.

In February, the corps consisted of the 1st, 2nd, 26th, 32nd, 41st, and 42nd Infantry Divisions. From February to July, 1918, the German Army launched four major offensives, attempting to secure victory before the full American forces could be mobilized. The final offensive, started in July 1918, was an attempt to cross the Marne, in the area of Château-Thierry, but I Corps and other formations on the American lines held, and the attack was rebuffed.

With the defeat of these German drives, I Corps conducted its first offensive mission, participating in the Second Battle of the Marne from 18 July until 6 August, which resulted in the reduction of the more important salients driven into Allied lines by the German offensives. After a brief period in the defensive sectors of Champagne and Lorraine between 7 August and 11 September, the corps took part in the St. Mihiel attack on 12 September, which reduced the German salient there during the next four days. Then followed another period on the defense in Lorraine as preparations advanced for what was to be the final Allied offensive of the war. On 26 September, I Corps troops began the attack northward that opened the Meuse-Argonne Offensive. From that day until 11 November 1918 when the war ended, I Corps was constantly moving forward.

The I Corps shoulder sleeve insignia was first worn by members of I Corps after approval from the AEF on 3 December 1918, but it was not officially approved until 1922. I Corps continued to train in France, until it was demobilized on 25 March 1919.

During its time in World War I, I Corps commanded the 1st, 2nd, 3rd, 4th, 5th, 6th, 26th, 28th, 32nd, 35th, 36th, 41st, 43rd, 77th, 78th, 80th, 82nd, 90th, 91st, 92nd Infantry Divisions at one point or another. Also assigned to the corps were the French 62nd, 167th and 5th Cavalry Divisions.

World War II

Lieutenant Colonel Steven Clay (Retd.) has traced the Corps' history in the interwar period. It was constituted in the Organized Reserve on 29 July 1921, allotted to the First Corps Area and assigned to the First Army. The Headquarters and Headquarters Company (HHC) were initiated by September 1922 at the Army Base, Boston, MA. The corps was assigned the 9th (Regular Army, Inactive) and 26th and 43rd Divisions (National Guard). (Clay Vol I 142) HHC, I Corps was withdrawn from the OR on 15 August 1927 and demobilized.

On 15 August 1927, XX Corps was reconstituted in the Regular Army. Two months later, on 13 October 1927, the XX Corps was redesignated as I Corps. However, the corps headquarters remained inactive during peacetime, until the US Army's buildup following the outbreak of War in Europe. On 1 November 1940, I Corps was reactivated at Columbia, South Carolina. For the next nine months, the corps supervised training and large scale divisional maneuvers.

New Guinea Campaign

On 6 July 1942 Lieutenant General Robert L. Eichelberger took command of the corps which he would lead through the majority of its service in the war. In the summer of 1942 the corps was ordered to Australia, closing into the area at Rockhampton on 17 October 1942. This move was to be part of a larger overall offensive in the south Pacific region. The corps at this time comprised the 41st and 32nd Divisions, engaged in the defense of British New Guinea, the beginning of the New Guinea campaign.Pimlott, p. 128. Though the Japanese advanced rapidly at first, a number of factors slowed their progress against the Allied forces. Stubborn resistance from two Australian brigades bought time for I Corps reinforcements to arrive while the terrain proved more difficult than the Japanese had anticipated. Supplies, which were already insufficient for the Japanese forces, were shortened even more as Japan's high command diverted them to the Guadalcanal campaign. The Japanese attack stalled, and once the threat of a Japanese invasion of Australia was abated, I Corps launched an offensive to push back the Japanese. With the 32nd Division and the 163rd Infantry Regiment of the 41st Division, the offensive was launched across the Owen Stanley Mountains of New Guinea. This force, later augmented by the Australian 7th Division, fought the Battle of Buna-Gona, slowly advancing north against a tenacious enemy under harsh weather and terrain conditions. Overstretched Japanese forces, low on supplies, were eventually overcome by US and Australian forces. Despite being surrounded, trapped, and outnumbered, the Japanese forces continued to fight until they were completely wiped out by Allied forces. Buna, on the north coast of the island, fell on 22 January 1943. The campaign was the first major Allied victory against the Japanese Army, and I Corps received the Distinguished Unit Citation. This victory marked the turn of the tide in the ground war against Japan.

After this campaign I Corps returned to Rockhampton, where it was engaged in the training of the Allied forces beginning to arrive in that area for the coming campaigns. From February 1943 until March 1944 I Corps prepared for its next assignment, Operation Cartwheel. That mission was the capture of Hollandia on the north coast of Dutch New Guinea; the units allocated to the corps for this task were the 24th and 41st Infantry Divisions.Pimlott, p. 129. The Task Force established itself ashore after a successful amphibious assault on 19 April 1944. It then began an offensive in that area to remove Japanese forces, before establishing air bases there. The battle was a vicious one; the jungles and swamps made difficult fighting ground, and it was not until 6 June that the area was secured. The entire Japanese 18th Army was cut off from its bases by the force. Following this campaign the corps directed the seizure of the island of Biak, which was secured by 24 June, to complete the advances necessary for the subsequent invasion of the Philippine Islands. On 20 August Major General Innis P. Swift succeeded General Eichelberger as commander of the corps.

Luzon

The corps was assigned to the Sixth United States Army in preparation for the offensive in the Philippines from the assets of the Philippine Commonwealth Army, Philippine Constabulary and the recognized guerrilla units. On 9 January 1945, I Corps successfully landed on the coast of the Lingayen Gulf in Northern Luzon with the mission of establishing a base for future operations to the north and of denying the enemy northern access to the South China Sea.Pimlott, p. 206. As a part of the Sixth Army with an overall force of 175,000 men, the American forces faced over 260,000 Japanese in Luzon.Horner, p. 60. In a sustained drive of thirty-four days which covered over 100 miles, I Corps crossed central Luzon and thus separated the Japanese forces in the north from those in southern Luzon, destroying Japanese armored units along the way. Additional landings at Samar and Palawan were conducted in February, reducing the pressure on the forces of I Corps. Following this accomplishment, the corps turned northward and began the systematic reduction of the enemy positions on the approach to the Cagayan Valley. The breakthrough into the valley was followed by a swift exploitation that took the corps to the north coast. This advance covered two hundred miles in little over 100 days; eliminating effective enemy resistance in northern Luzon. Manila was recaptured by the Allies after heavy fighting that ravaged the city. The intense fighting that ensued cost 8,000 killed and 30,000 wounded in the Sixth Army, compared to 190,000 dead for Japan. As the Sixth Army finished off the Japanese on Luzon, the Eighth United States Army

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