ON AT LEAST FOUR OCCASIONS during the forty years following the end of World War II the United States Army made major changes in its war-fighting doctrine. The first of these, completed in 1958, involved redesigning the structure of its combat divisions. The traditional structure developed during the war in Europe deployed 17,460 troops organized into three regiments (or brigades); each regiment in turn was organized into battalions. The division had a large number of vehicles (tanks and trucks) and its own antiaircraft forces. Organized in this way, a division could bring centrally controlled, massive firepower to bear on the enemy.
The new structure, called the "pentomic" division, was very different. It was smaller (13,748 men) and organized into five battle groups rather than three regiments; there were no battalion commanders. The number of vehicles was reduced and the division was stripped of its own antiaircraft artillery. The new form was designed to facilitate the decentralized and dispersed defense of an area by semiautonomous units that could fight more or less independently of each other. The avowed rationale for the reorganization and the tactical doctrine on which it was based was that the introduction of atomic weapons into the battlefield made the old structure outmoded; a massed force defending a defined geographic area would be a sitting duck for a nuclear attack. Skeptics who think that armies always prepare for the last war were confounded by the speed with which the army converted all fifteen of its divisions into the new pentomic form.
Within a few years, however, army leaders had become dissatisfied with the pentomic structure. A shortage of communications equipment made controlling the new-style division difficult under the best of circumstances and almost impossible in practice. The cutback in vehicles made it hard to deploy the battle groups. And so in the early 1960s a new doctrine was