The United States Department of Defense (DoD) is a vast federal agency responsible for coordinating and supervising all agencies and functions related to national security and the U.S. Armed Forces. Headed by the Secretary of Defense, who reports directly to the President, the DoD oversees over 1.4 million active-duty military personnel across six armed services, nearly 778,000 National Guard and reservists, and over 747,000 civilian employees, totaling more than 2.9 million personnel[2]. It includes three military departments—Army, Navy, and Air Force—and several key agencies such as the Defense Intelligence Agency, National Security Agency, and the Defense Advanced Research Projects Agency (DARPA), which focuses on cutting-edge military technology research[2]. Founded in 1947, the DoD has evolved into a global military force, charged with defending the U.S. homeland, projecting power abroad, and maintaining technological superiority. Its history is marked by significant achievements in military innovation, strategic defense initiatives, and global leadership in defense technology. Currently, the DoD is undergoing a major transformation initiative in 2025, aimed at streamlining workforce structures, reducing bureaucracy, and reallocating budgets to prioritize emerging threats and modern capabilities such as missile defense, nuclear modernization, and unmanned systems[1][3]. The Fiscal Year 2025 National Defense Authorization Act (FY25 NDAA) authorizes significant funding for modernization, including $143.8 billion for research and development and $33.5 billion for shipbuilding, emphasizing innovation and readiness[3]. A presidential executive order in 2025 mandates a sweeping reform of defense acquisition processes to accelerate procurement, enhance flexibility, and spur innovation within the defense industrial base[4]. This modernization effort reflects the DoD’s strategic emphasis on agility, speed, and technological edge in an increasingly complex global security environment. Notable aspects of the DoD include its integration of advanced technologies, such as AI-powered tools for operational effectiveness