Origins of operational depth in the First World War.

Modern scholarship on the Great War provided effective models on operational innovation and adaptation. However, the vital concept of operational depth remained unanalyzed. An examination of the challenge and response dynamic among the Germans, British, French, and United States' employment of fire support created the framework to examine this emergence. Each participant entered the war with unique theories that shaped their doctrine, structure, and tactics. After the onset of trench warfare, an attacker needed to penetrate an enemy's tactical depth into their operational depth faster than they could reinforce by rail. The Allies experimented with large concentrations of artillery, which led the Germans to develop a defense in depth. After a series of costly failures, the French and British countered this practice with a 'bite and hold' method that seized a piece of defensible terrain to defeat the clockwork German counterattack. The Germans chose the path of tactical excellence to achieve operational depth with the development of neutralization and infiltration tactics. The United States fused the 'bite and hold' with the principles of open warfare. Artillery served as the catalyst, problem, and solution that led to operational depth. The tenets of operational depth that stand out are the requirement for rearward depth, synchronization for the penetration, and forward depth. Rearward depth required logistical preparation, communications, and tactical dispersion. The initial penetration required a synchronized combined arms attack to move efficiently through the enemy's tactical depth. Forward depth relied on surprise, simultaneity, and mobility to draw combat power away from the point of penetration and continue the movement into the operational depth. An understanding of the emergence of operational depth and its principles serve as a model for incorporating new capabilities into modern warfare.