The C.I.A.’s response was unusual. Ordinarily, an agency served with a FOIA request is required to produce a list of relevant records. The agency must then release the listed records or cite specific legal justifications for keeping them secret. In the Glomar case, the C.I.A. argued that there were circumstances in which it was impossible for an agency to acknowledge even the existence of relevant records without also revealing some fact that the government had a right to withhold.

There are indeed cases in which merely confirming or denying the existence of certain records would reveal a classified fact, such as whether a particular person is a covert intelligence agent or the current target of lawful surveillance.

Those cases, however, are far less common than the C.I.A.’s increasingly frequent reliance on the Glomar doctrine would suggest. A study by the National Security Archive shows that federal court opinions cited the doctrine three times as often in the decade after 9/11 as in the quarter-century preceding it.

There has been a qualitative shift, too. Most of the cases before 2001, including the 1976 Glomar case, involved relatively narrow intelligence-gathering programs that were plainly within the C.I.A.’s mandate. More recently, the agency has used the Glomar doctrine to shield exceptionally controversial programs, and even unlawful conduct, including the torture and rendition of terrorism suspects.

The doctrine has also been invoked since 9/11 to shape public debate. A slew of administration officials have already spoken about the targeted killing program to reporters, both anonymously and on the record, and President Obama himself answered questions about the program during an online town hall. Thus the Glomar doctrine is not serving to keep the targeted killing program a secret, but rather to control which facts about the program are made public, and when. Not coincidentally, the C.I.A.’s reliance on the Glomar doctrine also makes it more difficult for individuals injured by the agency’s counterterrorism policies to challenge those policies in court.