Pentomic

Greek pent(e)- + -tome "of five parts") was a structure for infantry and airborne divisions adopted by the US Army between 1957 and 1963 in response to the potential use of tactical nuclear weapons on future battlefields.

[1] Several other countries also temporarily adopted similar structures in their armed forces, at around the same time as the US example, including France (from 1955), Australia, Turkey, and Spain.

During World War I the defensive firepower of infantry forces and especially their associated artillery made manoeuvrability almost impossible without overwhelming numbers.

By the start of World War II, this basic concept had developed into the idea of a "spearhead", a dense formation of highly mobile forces that would concentrate at a single point, overwhelm them locally, and then run into the lightly defended rear areas.

A single well-placed weapon could break up the attacking forces before they even had time to properly prepare, causing enough casualties to make them ineffective even in the defense.

In the battles foreseen by planners in the 1950s, traditional infantry and armored units appeared to be extremely vulnerable.

As part of this shift in policy, the majority of US military development and funding was sent to the US Air Force and US Navy; the Army was, to a degree, ignored.

[3] Westmoreland recalled that the pentomic structure, with all its flaws, was a creature of the Chief of Staff, and any officer who valued his career was loath to criticise it.

On 24 January 1957, the Secretary of the Army approved the U.S. Army Combat Arms Regimental System (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.

The 2nd Infantry Brigade was organized as follows:[7] 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".

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.

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.

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

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

The pentomic structure was abandoned in 1965, when the Spanish Army adopted the French doctrine and organization of the era.