Government Secrets Privilege
Government secrets privilege must first be differentiated from executive privilege. Executive privilege grants the executive branch confidentiality with regards to its deliberative process. The state secrets privilege is an absolute privilege to proscribe the disclosure of military or diplomatic secrets. There are two sources for this privilege; the Common Law privilege and that granted by the Classified Information Procedure Act (CIPA).
Common law government secrets privilege
While this privilege has existed for some time in English law, the seminal case in U.S. precedent is that in United States v. Reynolds. In that case, three civilian observers on a military plane testing top-secret material died when the plane crashed. The widows sued for damages, but were not granted access to top-secret documents during the discovery process. The Court ruled that the privilege does exist, that is belongs to the Government and that no private party can claim or waive it. The privilege must be actively claimed by the relevant department
United States v. Reynolds, 345 U.S. 1 (1952)