Mouwembleem 1st Corps (Sleeve patch 1st Corps green backing)

I Corps "America's 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 Forces Command.

I Corps' current mission is part of the United States' Asia-Pacific Shift. The Pacific Rim Rebalance will involve several combined and joint military exercises in Japan, Korea,Thailand, Philippines, and Australia. Part of I Corps' objectives for these exercises will be Joint Task Force certification in support of United States Pacific Command missions.

Activated in World War I in France, I Corps oversaw US Army divisions as they repelled several major German offensives and led them 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 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 commanding headquarters in the occupation of Japan.

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. 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 Presidential 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. 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. Swiftsucceeded 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. 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. 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 in the south sent units all throughout the Philippines to eliminate remaining Japanese resistance on the islands. TheTenth United States Army in the north commenced securing Okinawa and Iwo Jima. With the defeat of the Japanese at each of these places, the US forces had locations from which to launch attacks into mainland Japan.

Allied forces then began preparing for the invasion of mainland Japan, Operation Downfall. I Corps was assigned as one of four Corps under the command of the Sixth Army, with a strength of 14 divisions. I Corps was to lead the assault on Miyazaki, in southern Kyūshū, with the 25th, 33rd, and 41st Infantry Divisions. Opposing them would be the Japanese 57th Army, with the 154th, 156th, and 212th Japanese Infantry Divisions. Before the assault could be launched, Japan surrendered, following the use of nuclear weapons on Hiroshima and Nagasaki.

During World War II, the 6th, 8th, 9th, 24th, 25th, 30th (during training in U.S. only?), 32nd, 33rd, 37th, 41st, 43rd, 77th and 98th Infantry Divisions were assigned to I Corps at one time or another, along with the 2nd Marine Division, 7th Australian Division, and elements of the 11th Airborne Division.

Occupation of Japan

After the end of hostilities, I Corps was assigned to occupation duty in Japan. On 19 September 1945 the corps, with the assigned 33rd Infantry Division, sailed from Lingayen Gulf for Japan, landing on the island of Honshū on 25 September, three weeks after Japan's formal surrender. 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.

By 1948, as the purely occupational mission was accomplished, troops of the corps focused more military training and field exercises designed to prepare them for combat. Its force was eventually downsized to the 24th Infantry Division on Kyūshū and 25th Infantry Division on mid-Honshū. The US Army continued a slow and steady process of post-war drawdown and demobilization on its own, and on 28 March 1950, the corps was formally inactivated in Japan, and its command consolidated with other units.