Pentomic

Pentomic (cf.Greek pent(e)- and -tome, "of five parts") refers to a structure for infantry divisions adopted by the U.S. Army in 1957 in response to the perceived threat posed by tactical nuclear weapons use on the battlefield.

"Pentomic Division" was "a public relations term designed to combine the concept of five subordinate units ('penta') with the idea of a division that could function on an atomic or nonatomic battlefield."

Organization
The official name of this structure was ROCID—Reorganization of the Current Infantry Division. However, it was generally known as the Pentomic Division. The Pentomic structure was a reaction to the perceived threat of Atomic weapons on the modern battlefield and a chance for the Army to secure additional funding.

Previously the US Army had fought World War I with the "square" organisation, every unit having four subunits. Prior to American participation in the Second World War the organisation was changed to "triangular"; with every unit generally having three subunits.

The standard infantry division was seen as being too clumsy in its fixed organization. Units were organized in a system of "5's". A division was organized with five battle groups, each commanded by a colonel. Each battle group consisted of four line (rifle) companies, a mortar (4.2) battery, and a Headquarters company with signal, assault gun and recon platoons. Each company was commanded by a captain. Artillery battalions were organized with five batteries—four were howitzers, the fifth was a mortar battery. The addition of "Davy Crockett" recoilless spigot guns with atomic warheads brought the army into the atomic age. Figure 2, "The Pentomic Division", on page 107 of Bacevich's book "The Pentomic Era" shows a graphic from the "Annual Report of the Secretary of Defense for Fiscal Year 1956". The graphic shows "5 Combat Groups of 5 Companies Each"; 5 105mm Mortar Batteries; an Honest John Rocket Battery; 5 105mm Howitzer Batteries; and, 5 HQ & Service Companies, with each including "Reconnaissance, Signal, Supply, & Medical".

The pentomic division very closely resembled the wartime 82nd and 101st Airborne Divisions which had each fought with five parachute or glider infantry regiments. Their regiments were smaller and more austere than the regular infantry regiments of the infantry divisions. This was no accident as the top leaders of the army at this time were all airborne Generals—Ridgway, Taylor, and Gavin. The armored divisions were not affected as their three combat commands were considered appropriate for the nuclear battlefield.

Implementation
In July 1955 General Taylor became the Chief of Staff of the United States Army where he selected General William Westmoreland as his Secretary to the General Staff. Westmoreland recalled that Taylor was told by President Dwight Eisenhower he had to do something to give the Army "charisma"; something in Westmoreland's words to give the Army a "modern look". In the mid 1950s the Army was facing a loss of morale following the end of the Korean War when the lion's share of government funding and publicity was going to the nuclear armed United States Air Force and Navy. After Taylor designed the Pentomic concept he promoted Westmoreland to what was then the youngest Major General in the US Army to command Taylor's former wartime command the recently reactiviated 101st Airborne Division that would be the first unit to be reconfigured in the Pentomic structure.

American army officers felt the plan was "ill started, ill fated and hopefully short lived" with some thinking it was a scheme of Taylor's to increase the number of active divisions in the army when he had actually cut their combat manpower.

Westmoreland recalled that as the Pentomic structure with all its flaws was a creature of the Chief of Staff, any officer who valued his career was loathe to be heard to criticise it. Westmoreland also briefed all officers in the division "Our job is not to determine whether it will work-our job is to make it work". Following the end of Westmoreland's command of the 101st in 1960 he recommended the pentomic structure be abolished.

Lineages & honors
When the U.S. Army division was reorganized under the Pentomic structure in 1957, the traditional regimental organization employed by the Army was to be eliminated. This raised questions as to what the new units were to be called, how they were to be numbered, and what their relationship to former organizations was to be. Many of the Army's senior officers were determined to perpetuate the historic lineages of the Army, unlike the situation after the Civil War when the Grand Army of the Republic persuaded Congress to forbid the linkage between the Civil War era Union Army Corps and the new Corps organized for the Spanish American War.

On 24 January 1957 the Secretary of the Army approved the CARS concept, as devised by the Deputy Chief of Staff for Personnel, which was designed to provide a flexible regimental structure that would permit perpetuation of unit history and tradition in the new tactical organization of divisions, without restricting the organizational trends of the future.

Separate brigades were organized with two or three battle groups. The 2nd Infantry Brigade was organized as follows:
 * Headquarters & Headquarters Company
 * 1st Battle Group, 4th Infantry
 * 2nd Battle Group, 60th Infantry
 * 1st Battalion, 76th Artillery
 * Company F, 34th Armor
 * Company G, 34th Armor
 * Brigade Trains
 * ??th Engineer Company
 * ??th Engineer Company
 * Troop F, 5th Cavalry

Flaws
The Pentomic systems was found to be flawed in several ways.
 * Training: Officers would command with long periods of time between assignments to maneuver units. This would erode the experience and competence of Battle Group commanders once the experienced officers of World War II and Korea retired.
 * Span of control: Most people are capable of managing 2–5 separate elements. The pentomic battle group contained seven companies and in combat would habitually have 2–4 more attached such as engineers, artillery, or armor.
 * Loss of regimental cohesion: Traditional infantry regiments had long histories and commanded strong loyalty from their assigned soldiers. The Battle Groups, and later, the ROAD brigades, combined infantry battalions from different regiments in a chaotic fashion that eliminated regimental cohesion.
 * Loss of a level of command: Previously there had been Company Commanders (Captain), Battalion Commanders (Major or Lieutenant Colonel), and Regimental Commanders (Colonel); the Pentomic structure eliminated the level of Battalion Commander.

End of ROCID
In December 1960, the Army began studying proposals to reorganize again that was hastened by newly elected President John F. Kennedy's "Doctrine of Flexible Response". This led to the ROAD (Reorganization Objective Army Division) initiative by 1963.

Other nations
The Australian Army implemented a similar structure, called the Pentropic organisation, between 1960 and 1965 but reverted to its previous structure after experiencing difficulties similar to those experienced by the U.S. Army.

The New Zealand Army planned to reorganize its forces around a derivative of the Australian concept, but the Australians abandoned the concept before the New Zealanders could start the change.

The Turkish Army utilised the pentomic structure in 1960s for a period before adopting the American ROAD divisional organisation.

The West German Army attempted reorganization around the pentomic structure in 1957, abandoning the idea in a few years.