Nuclear weapons life extension and countering nuclear threats will continue to be a central concern for the United States and the Department of Defense. The Department has identified the dual missions of sustaining a safe, secure, and effective nuclear deterrent and countering the threat from nuclear terrorism and nuclear proliferation as among the most important for U.S. national security priorities. Nuclear Matters serves as the focal point for these missions within the Department of Defense.
"To deter nuclear war and serve as last resort weapons of self-defense. In this sense, U.S. nuclear weapons are fundamental to our nation's security and have historically provided a deterrent against aggression and security assurance to U.S. allies. A robust, flexible, and survivable U.S. nuclear arsenal underpins the U.S. ability to deploy conventional forces worldwide; provides the Commander-in-Chief with credible response options to strengthen deterrence; and supports U.S. nonproliferation goals by extending deterrence to allies, thereby dissuading them from developing their own nuclear weapons."
Secretary of Defense Mattis at his confirmation hearing, January, 2017