Short answers, pulled from the story.
The Department of Defense was officially established on the 10th of August 1949, having previously operated as the National Military Establishment since the 18th of September 1947. The National Security Act of 1947 created the National Military Establishment on the 26th of July 1947 before the name change occurred two years later.
The Department of Defense spent $886 billion in fiscal year 2024 and failed its fifth consecutive audit as of 2022. Officials cannot track more than 60 percent of the department's $3.5 trillion in assets due to systemic financial disarray.
The secretary of defense serves as the cabinet-level head of the Department of Defense and is appointed by the president with Senate confirmation. The operational chain of command runs from the president to the secretary of defense and then to the commanders of the eleven unified combatant commands.
The Department of Defense oversees the Defense Intelligence Agency, the National Security Agency, the National Geospatial-Intelligence Agency, and the National Reconnaissance Office. These agencies handle signals intelligence, geospatial intelligence, and measurement and signature intelligence under the direction of the under secretary of defense for intelligence and security.
The Department of Defense employs over 2.91 million people including 1.4 million active-duty uniformed personnel as of November 2022. The six armed services include the Army, Navy, Marines, Air Force, Space Force, and the Coast Guard for certain purposes.