Pentomic

Pentomic (cf. 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. It was intended that the five subordinate units, which were often referred to as battle groups (to distinguish them from traditional units), would be able to deploy and engage in operations more rapidly than conventional brigades, whilst also having greater offensive capabilities than conventional battalions. One US Army publication defines the pentomic division as "a public relations term designed to combine the concept of five subordinate units ('penta') with the idea of a division that could function on [either] an atomic or nonatomic battlefield". 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. The addition of mechanization to army forces led to rapid changes in doctrine. During World War I the defensive firepower of infantry forces and especially their associated artillery made manoeuvrability almost impossible without overwhelming numbers. Any breakthrough could be countered by reserve forces that moved at the same speed as the attacking forces. With the introduction of the first tanks, much smaller forces could effect a breakthrough, and move much more rapidly than the defending infantry. Ideally, this would force the defenders to retreat to new lines in order to maintain a front line. 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. This became known as Blitzkrieg after its initial successful employment by the German forces. Nuclear weapons dramatically upset this concept.