Short answers, pulled from the story.
The Department of Defense formally began operations on the 18th of September 1947. The National Security Act of 1947 established the National Military Establishment which James V. Forrestal led as the first secretary of defense. Congress renamed this entity to the Department of Defense on the 10th of August 1949.
The secretary of defense serves as the head of the Department of Defense and reports directly to the president who remains commander-in-chief of all U.S. Armed Forces. Operational command authority flows from the president to the secretary of defense and then to commanders of Combatant Commands following the Goldwater-Nichols Act in 1986.
Four national intelligence services operate under DoD jurisdiction including the Defense Intelligence Agency, National Security Agency, National Geospatial-Intelligence Agency, and National Reconnaissance Office. These organizations work together to provide comprehensive intelligence coverage for military operations worldwide while fulfilling requirements for national policymakers and war planners.
Fiscal year 2019 budget totaled approximately $686 billion in discretionary spending plus $8.99 billion mandatory spending reaching $695 billion combined total. This figure represented 3.15% of gross domestic product accounting for approximately 38% of global military budgeted spending combined with the next seven largest militaries.
Department officials annually report to Congress that their books exist in such disarray that conducting proper audits proves impossible. The department failed its fifth consecutive audit in 2022 unable to account for more than 60% of its $3.5 trillion asset portfolio due to systemic problems preventing accurate financial tracking across massive organizational structures spanning decades.