Since its initial formal issuance in 1954, Department of Defense Directive (DoDD) 5100.01, “Functions of the Department of Defense and Its Major Components” has undergone both minor and substantial revisions as it outlines the primary functions of the Department of Defense. The directive derived from roles and missions discussions, following World War II, which aimed to delineate the purposes of, improve joint operations between, and inform resourcing the Military Services. To date, major organizational and functional changes within the Department of Defense have been almost exclusively due to specific and significant Congressional or Secretary of Defense direction in response to notable failures in coordinated operations between the Military Services. There have been no updates during major conflicts. The most recent major update of December 21, 2010, which reflected the results of the Congressionally-directed DoD 2009 Quadrennial Roles and Missions Review, primarily recorded the evolution of the Department’s mission areas rather than promulgating any major adjustments.