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Pentomic (cf.Greek pent(e)- and -tome, "of five parts") refers to a structure for infantry and Airborne 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."[1]



The infantry and airborne division structures commonly known as Pentomic divisions are actually two related organizations, officially known as Reorganization of the Airborne Division (ROTAD) and Reorganization of the Current Infantry Division (ROCID). The Pentomic structure was a reaction to the perceived threat of nuclear weapons on the modern battlefield and a chance for the Army to secure additional funding.

Earlier the US Army had fought World War I with the "square" organisation, each division having two brigades, each with two infantry regiments. Prior to American participation in the Second World War the organization was changed to "triangular" with each division directly controlling three regiments, and eliminating the brigade echelon from the division.

1960 Pentomic Infantry Division. The five "Battle Groups" on the left of the diagram dominate the Divisional structure.

The ROTAD was implemented first, with the 101st Airborne Division reorganizing under test tables of organization published on 10 August 1956. The core of the division was five infantry battle groups, each containing five infantry companies, a headquarters and service company, and a mortar battery. A headquarters and headquarters battalion contained a headquarters and service company, an administration company, an aviation company and a reconnaissance troop. The division artillery contained a headquarters and headquarters battery, five 105mm howitzer firing batteries, and an Honest John missile battery. A support group contained a headquarters and service company, a maintenance battalion, a quartermaster parachute company, a supply and transportation company, and a medical company. Separate signal and engineer battalions completed the organization, which required a total of 11,486 men. After a series of tests by the 101st Airborne Division, the Continental Army Command (CONARC) approved slightly modified tables of organization, and all three airborne divisions (the 11th, 82nd and 101st) were reorganized during 1957.[2][3]

Shortly after the 101st began testing ROTAD, the CONARC began developing ROCID, forwarding the initial ROCID tables of organization to the Army Staff on 15 October 1956. The core of this initial ROCID organization, similar to ROTAD, consisted of five battle groups, each with a headquarters and service company, a mortar battery and four infantry rifle companies. The Division Artillery was organized with a 105mm howitzer battalion, with five firing batteries, and a composite battalion with four firing batteries: two 155mm howitzer batteries, an 8in howitzer battery and an Honest John missile battery. In addition to a headquarters and headquarters company, a tank battalion, reconnaissance squadron, engineer battalion, signal battalion and division trains completed the division’s organization. The division trains consisted of a headquarters and headquarters detachment (which included the division’s band), an ordnance maintenance battalion, a medical battalion, a transportation battalion, a quartermaster company, an aviation company and an administrative company. The Army’s nine infantry divisions completed reorganization into the new structure in 1957.[4][5][6][7]

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 five line (rifle) companies, a mortar (4.2 in) battery, and a headquarters company with signal, assault gun and recon platoons. Each company was commanded by a captain. The Division Artillery was initially organized with a 105mm howitzer battalion, with five batteries, and a composite battalion with four firing batteries: two 155mm howitzer batteries, an 8in howitzer battery and an Honest John missile battery. Later, the Division Artillery was re-organized into five direct support battalions (each with one 105mm firing battery and one 155mm firing battery), and a general support battalion (with the 8in firing battery and the Honest John battery). Two of the direct support battalions were equipped with self-propelled howitzers, and three were equipped with towed howitzers. In order to man the increased number of batteries, the 4.2in mortar batteries in each battle group were removed.[8] The 1961 addition of "Davy Crockett" recoilless spigot guns with atomic warheads supplemented the concept of the atomic age army. 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" depicting the initial ROCID organization. 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".[9]

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 commanders—Matthew Ridgway, Maxwell D. Taylor, and James M. Gavin. The armored divisions were not affected as their three combat commands were considered appropriate for the nuclear battlefield.


US 3rd Infantry Division, Pentomic Structure, August 1960. Each of the five Infantry "Battle Groups" on the left contain five infantry companies. The five groups of five define the Pentomic structure.

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.[10]

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.[11]

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 loath to be heard to criticise it.[12] 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.[13]


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.[14]

Separate brigades were organized with two or three battle groups. The 2nd Infantry Brigade was organized as follows:[15]


The Pentomic systems was found to be flawed in several ways.

  • Training: Officers would not command for long periods of time between assignments to maneuver units (as a Captain at the company level and as a Colonel at the battle group level). 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.[16]

End of ROCIDEdit

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 nationsEdit

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.[17]

The Turkish Army utilised the pentomic structure in 1960s for a period before adopting the American ROAD divisional organisation.[18]

The West German Army attempted reorganization around the pentomic structure in 1957, abandoning the idea in a few years.[19]

After the signature of the Pact of Madrid with the United States, the Spanish Army abandoned the organization inherited from the Spanish Civil War to adopt the pentomic structure. Three experimental pentomic infantry divisions were created in 1958, followed by five additional ones in 1960. The pentomic structure was abandoned in 1965, when the Spanish Army adopted the French doctrine and organization of the era.[20]

See alsoEdit


  1. ^ Johnathan M. House, Toward Combined Arms Warfare: A Survey of 20th-Century Tactics, Doctrine, and Organization, 1984. United States Army Combat Studies Institute. US Army Command and General Staff College. Fort Leavenworth, Kansas. p. 155.
  2. ^ Directory and Station List of the United States Army, 15 August 1957
  3. ^ Wilson, John B. Maneuver and Firepower: The Evolution of Divisions and Separate Brigades (CMH Pub 60-14-1). Army Lineage Series. Washington: Center of Military History: 272-276.
  4. ^ McKenney, Janice E. The Organizational History of Field Artillery, 1775–2003 (CMH Pub 60-16). Army Lineage Series. Washington: Center of Military History, 2007: 250-252.
  5. ^ Directory and Station List of the United States Army, 18 February 1957
  6. ^ Directory and Station List of the United States Army, 15 August 1957
  7. ^ Directory and Station List of the United States Army, 17 February 1958
  8. ^ McKenney, Janice E. The Organizational History of Field Artillery, 1775–2003 (CMH Pub 60-16). Army Lineage Series. Washington: Center of Military History, 2007: 250-252.
  9. ^ "The Pentomic Era". 1986. Retrieved 5 March 2011. 
  10. ^ pp. 44-46 Sorley, Lewis Westmoreland: The General Who Lost Vietnam Houghton Mifflin Harcourt, 11/10/2011
  11. ^ p.178 Linn, Brian McAllister The Echo of Battle: The Army's Way of War Harvard University Press, 30/06/2009
  12. ^ Lewis, Adrian R. The American Culture of War: A History of US Military Force from World War II to Operation Enduring Freedom Routledge, 11/01/2013
  13. ^ p.75 Mrozek, Donald J. Air Power and the Ground War in Vietnam The Minerva Group, Inc., 01/06/2002
  14. ^ "The Pentomic Era". June 1952. Retrieved 5 March 2011. 
  15. ^ Directory and Station List of the United States Army, 15 August 1960
  16. ^ "The Pentomic Era". June 1952. Retrieved 5 March 2011. 
  17. ^ Damien Marc Fenton, 'A False Sense of Security,' Centre for Strategic Studies:New Zealand, 1998, appendix
  18. ^ British Military Attache's Annual Report on the Turkish Army, Annex A to DA/48, dated 30 March 1974, FCO 9/2127 via Public Record Office, Kew
  19. ^ "West Germany: The Pentomic Army". Time. June 1957. Retrieved 5 March 2011. 
  20. ^ PUELL DE LA VILLA, Fernando (2010). "El devenir del Ejército de Tierra (1945-1975)". In Fernando Puell de la Vega y Sonia Alda Mejías (ed.). Los Ejércitos del franquismo. Madrid: IUGM-UNED. 2010. Pp. 63-96.

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