The United States Department of Energy (DOE) is a cabinet-level federal department responsible for the nation's energy policy and nuclear safety. It manages the nuclear weapons stockpile, nuclear propulsion reactors for Navy aircraft carriers and submarines, energy conservation programs, energy-related research and development, radioactive waste disposal, and domestic energy production. DOE operates 17 national laboratories that conduct research in physics, materials science, energy technologies, and environmental management. Its primary customers include other federal agencies, the U.S. military, industry partners through grants and contracts, and the public via regulatory oversight and programs. The department targets the U.S. energy sector encompassing fossil fuels, renewables, nuclear power, and efficiency improvements. DOE's annual budget exceeds $40 billion, supporting over 15,000 employees and tens of thousands at national labs. It administers the Advanced Research Projects Agency-Energy (ARPA-E) for high-risk energy innovations and leads nonproliferation efforts.