The Three Block War is a concept described by U.S. Marine General Charles Krulak in the late 1990s to illustrate the complex spectrum of challenges likely to be faced by Marines on the modern battlefield. In Krulak's example, Marines may be required to conduct full scale military action, peacekeeping operations and humanitarian aid within the space of three contiguous city blocks. The thrust of the concept is that modern militaries must be trained to operate in all three conditions simultaneously, and that to do so, leadership training at the lowest levels needs to be high. The latter condition caused Krulak to invoke what he called "strategic corporals"; low-level unit leaders able to take independent action and make major decisions.
The term has been referenced by CENTCOM commander General James Mattis, and has also been adopted by the British military, including former Chief of the General Staff, General Sir Mike Jackson and former Defence Secretary Geoff Hoon, and also by former Canadian Chief of Defence Staff Rick Hillier.
The strategic corporal is the notion that leadership in complex, rapidly evolving mission environments devolves lower and lower down the chain of command to better exploit time-critical information into the decision making process, ultimately landing on the corporal, the lowest ranking non-commissioned officer, typically commanding a fire team of 4 individuals or a squad of 13 individuals (three fireteams plus NCO). In very rapidly evolving mission situations, obtaining mission instructions from remotely located command may result in mission failure, or in casualties to both force personnel and civilians. Conversely, misusing this kind of responsibility may result in personal liability for the team leader: a decision executed to respond to situational needs may result in later prosecution as the team leader's actions are reviewed by higher authorities.