Department of Defense

The Department of Defense is the largest employer in the world, with 1.3 million active-duty service members, 750,000 civilian employees, and 800,000 reserve and National Guard personnel. Its budget — the largest discretionary spending category — covers military operations, weapons systems development and procurement, base maintenance, and personnel costs including pay and healthcare. The DOD also funds advanced research through DARPA, which has historically produced technologies like the internet and GPS that later transformed civilian life.