National Defense is the single largest discretionary spending line in the federal budget — roughly $874 billion in FY2024, or about 13% of all federal outlays. The bulk goes to the Department of Defense across four main buckets: operations and maintenance (bases, training, fuel, healthcare for service members), military personnel (pay and allowances for active-duty service members), procurement (the actual weapons, aircraft, ships, and vehicles), and research and development of next-generation systems.
A smaller slice (~$35B) flows through the Department of Energy for nuclear weapons activities — stockpile maintenance, naval reactors, and defense-related cleanup at DOE labs. Defense-related intelligence community work (parts of NSA, FBI counterintel) also counts toward this function.
On the contractor side, five companies dominate: Lockheed Martin (F-35 fighters, missile defense, Sikorsky helicopters), RTX/Raytheon (Patriot/THAAD missiles, Pratt & Whitney engines), General Dynamics (submarines, Abrams tanks), Boeing's defense arm (KC-46 tankers, Apache helicopters), and Northrop Grumman (B-21 bomber, missile defense radars). Together they receive over $130 billion in annual prime contract obligations.