Question: Is the 72nd field brigade part of the oldest or newest established field army?
Context: The history of the Arkansas Army National Guard and the Cold War involves several statewide re-organizations that occurred as a result of the evolving structure of United States Army Divisions and Brigades.  In 1959 the state re-organized and restationed units in response to the Army's adoption of the Pentomic Division, the structure which was designed to counter the Soviet threat in eastern Europe.  Several Arkansas National Guard units were mobilized in 1960 as part of the Berlin Crisis.  In 1963 the state reorganized again as the administration of President John F. Kennedy focused on "Flexible Response" and divisions reorganized to meet the challenged of numerous small wars such as the war in Vietnam.  In 1967 the 39th Infantry Division was reorganized as the 39th Infantry Brigade (Separate) as a result of a plan to reduce the total number of National Guard Divisions nationwide.  The state would eventually gain a new headquarters, the State Area Command in order to provide a higher headquarters for several units which were not assigned to either the 142nd Field Artillery Brigade or the 39th Infantry Brigade (Separate). The First Army is the oldest and longest established field army of the United States Army, having seen service in both World War I and World War II, under some of the most famous and distinguished officers of the U.S. Army.  It now serves as a mobilization, readiness and training command. The 72nd Guards Joint Training Centre is a training centre of the Belarus Armed Forces.  It trains warrant officers and junior specialists for the Belarus Armed Forces and is based in Borisov.  The centre is currently led by Colonel Igor Korol.  The 72nd Guards Joint Training Centre traces its history back to the Soviet 120th Rifle Division.  For its actions during the Yelnya Offensive, the division became the 6th Guards Rifle Division in September 1941.  In November 1945, the division became the 15th Guards Mechanized Division.  On 15 May 1957, it became the 47th Guards Tank Division.  The division became a training unit in 1960 and was renamed the 45th Guards Tank Training Division in 1965.  In 1987, it became the 72nd Guards District Training Centre.  In 1992, it was taken over by Belarus and became the 72nd Guards Joint Training Centre. Third Military Medical University (中国人民解放军第三军医大学) is a Chinese military institution of higher learning, affiliated to the People's Liberation Army (PLA).  It is located in Chongqing, and was founded in 1954, by the merger of former Sixth and Seventh Medical Universities.  The predecessor of the Sixth Medical University was Military Medical School of 4th Field Army of PLA and Nanchang Medical College (former Zhongzheng Medical College).  The Seventh Medical University originated from the Medical School of Taiyue Military Region (Later the Medical College of 2nd Field Army of PLA).  After merging, the school was named "Seventh Military Medical University".  It was relocated to Shanghai in 1969, but moved back to Chongqing in 1975, when the Central Military Commission of PLA renamed it "Third Military Medical University". The 72nd Field Artillery Brigade is an AC/RC unit based at Joint Base McGuire-Dix-Lakehurst, New Jersey.  The unit is responsible for training selected United States Army Reserve and National Guard units along the East coast.  The brigade is a subordinate unit of First Army Division East, First United States Army. The 142nd Field Artillery Regiment ("Second Arkansas") is a United States Army field artillery regiment currently represented in the Arkansas Army National Guard by the 1st Battalion, 142nd Field Artillery, headquartered in Harrison, Arkansas, 2nd Battalion, 142nd Field Artillery, headquartered in Fort Smith, Arkansas and Battery F (Target Acquisition), 142nd Field Artillery stationed in Fayetteville, Arkansas, elements of the 142nd Fires Brigade which is headquartered in Fayetteville, Arkansas.  The regiment was created in 1917 from the former 2nd Arkansas Infantry.  The 142nd Field Artillery shipped to France during World War I, but did not see combat before cessation of hostilities.  The regiment was activated for World War II, but its battalions were redesignated as separate battalions, 1–142nd became the 936th Field Artillery Battalion, the 2–142nd became the 937th Field Artillery Battalion.  The battalion's served throughout the European Theater of Operations.  The battalions were activated again for the Korean War and served throughout the war.  Following the Korean War the separate battalions resumed their former designations of 1–142nd FA and 2–142nd FA.  The 142nd Field Artillery Brigade, including both battalions was activated for Operation Desert Storm.  Elements of the 142nd Fires Brigade have been activated for service in Operation Noble Eagle and Operation Iraqi Freedom.  The 142nd Fires Brigade was instrumental in support and recovery operations located in New Orleans, Louisiana after hurricanes Katrina and Rita devastated the Gulf Coast. The 72nd Indian Infantry Brigade was an infantry brigade, of both the British and Indian Armies, formed in the United Kingdom in January 1941 during the Second World War.  On 1 June 1943 it was re-designated as the British 72nd Infantry Brigade. The 157th Maneuver Enhancement Brigade, also known as the Iron Brigade, is based out of Milwaukee, Wisconsin.  It was formerly known as the 57th Field Artillery Brigade, at which time its subordinate organizations included the 1st Battalion, 126th Field Artillery Regiment and the 1st Battalion, 121st Field Artillery Regiment from the Wisconsin Army National Guard, plus the 1st Battalion, 182nd Field Artillery Regiment of the Michigan Army National Guard.  Not to be confused with the famous "Iron Brigade" of the Civil War, the 57th Field Artillery Brigade is also known as the "Iron Brigade," a nickname traditionally given to crack artillery units in the Civil War.  It was during World War I that the 57th Field Artillery Brigade earned its nickname as it spent many hours at the front and fired more artillery rounds than any brigade in the American Army. The 402nd Field Artillery Brigade has been absorbed into the 5th Armored Brigade (United States).  The 402nd was an AC/RC/NG unit based at Fort Bliss, Texas.  The unit is responsible for training selected United States Army Reserve & Army National Guard units along the West coast.  The unit was formerly designated as 3rd Brigade, 91st Infantry Division, and as the 402nd Brigade (Training).  The Brigade is a subordinate unit of the First United States Army (First Army Division West).  From 1985 to 1996, the Brigade conducted artillery training at Fort Sill, Oklahoma. The 102nd Field Artillery Regiment was organized in July 1786 in the Massachusetts Volunteer Militia at Salem, Massachusetts as the Cadet Company and re-designated as the Second Corps of Cadets.  In 1972 they became the 102nd Field Artillery and in 1996 the 102nd was reorganized as a regiment to consist of the 1st Battalion.  The regiment's battalions were associated with the 26th Infantry Division for a long period and later was assigned to the 113th Field Artillery Brigade.  On July 15, 2006, the 102d cased their colors in Fort Independence at Castle Island in South Boston, Massachusetts.  The lineage of the 102d Field Artillery and the Second Corps of Cadets was transferred to Alpha Battery, 1st Battalion 101st Field Artillery in Danvers, Massachusetts.
Answer: the oldest