In 1973, the ship Glomar Explorer was built by Sun Shipbuilding and Drydock Co and Howard Hughes. Its purpose and mission was for the CIA to raise a sunken Russian nuclear submarine. The project was classified, but the LA Times broke the story in 1975. The CIA began to urge reporters not to report on the ship for reasons of national security. A curious reporter filed a FOIA request to obtain CIA records of attempts to quash the press in regards to reports on this vessel.

The CIA responded by refusing to neither confirm nor deny the existence of any responsive records. The CIA claimed that any records that might exist which may reveal any CIA connection with or interest in the activities of the Glomar Explorer, or any evidence that might reveal the existence of records of this type would be classified, and therefore, exempt from disclosure under exemption 1 of the FOIA. They also insisted that exemption 3 applied, as the National Security Act of 1947 precluded them from releasing information related to the functions of CIA personnel.

The Glomar response, by which the agency neither admits nor denies that it possesses a requested document, traces its roots to Phillippi v. CIA, 546 F.2d 1009 (D.C. Cir. 1976).

Ever since then, the terms "Glomar response," and "Glomarization" are used to describe any agency’s response when they can "neither confirm nor deny" whether something exists or not. It's relatively rare, and usually questionable or suspicious. The US government uses it in a variety of ways, to respond to questions about secret military installations to the existence of torture documents.

The US Department of the Interior even spells it out on their webpage:

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