The United States National Nuclear Security Administration (NNSA) is part of the United States Department of Energy. It works to improve national security through the military application of nuclear energy. The NNSA maintains and improves the safety, reliability, and performance of the United States nuclear weapons stockpile through the use of science, technology, and engineering. It is also responsible for many nuclear nonproliferation, counter-terrorism, counter-proliferation, and radiological emergency response efforts for the United States, along with the naval reactors for the United States Navy.