Critical Nuclear Weapon Design Information (CNWDI, often pronounced SIN-widdy or SIN-wuh-dee) is a U.S. Department of Defense (DoD) category of Top Secret Restricted Data or Secret Restricted Data that reveals the theory of operation or design of the components of a thermonuclear or fission bomb, warhead, demolition munition, or test device. Specifically excluded is information concerning arming, fuzing, and firing systems; limited life components; and total contained quantities of fissionable, fusionable, and high explosive materials by type. Among these excluded items are the components that DoD personnel set, maintain, operate, test or replace. The sensitivity of DoD CNWDI is such that access is granted to the absolute minimum number of employees who require it for the accomplishment of assigned responsibilities on a classified contract. Because of the importance of such information, special requirements have been established for its control.