delivered the opinion of the Court.
Thе Freedom of Information Act (FOIA), 5 U. S. C. § 552 (1982 ed.), requires federal agencies to disclose records 1 that *794 do not fall into one of nine exempt categories. 2 The question presented is whether confidential statements obtained during an Air Force investigation of an air crash are protected from disclosure by Exemption 5, which exempts “inter-agency or intra-agency memorandums or letters which would not be *795 available by law to a party other than an agency in litigation with the agency.”
I
On October 9, 1973, the enginе of an Air Force F-106B aircraft failed in flight. Captain Richard Hoover, the pilot, was severely injured when he ejected from the plane. Under Air Force regulations, the incident was a significant air crash that required two separate investigations: a “collateral investigation” and a “safety investigation.”
The collateral investigation is conducted “to preserve available evidence for use in claims, litigation, disciplinary actions, аdministrative proceedings, and all other purposes.” 3 Witnesses in a collateral investigation testify under oath and generally are protected by the procedural safeguards that are applicable in other formal hearings. The record of the collateral investigation is public.
The safety investigation is quite different. It is conducted by a specially appointed tribunal which prepares a report that is intended for “the sole purpose of taking corrective action in the interest of accident prevention.” 4 To encourage witnesses to speak fully and frankly, they are not sworn and receive an assurance that their statements will not be used for any purpose other than accident prevention. 5 Air Force regulations contain a general prohibition against the release of safety investigation reports and their attachments, 6 subjeсt to an exception which allows the Judge Advocate General to release specified categories of “factual material” and “nonpersonal evidence.” 7
*796 After the collateral and safety investigations had been completed, Captain Hoover filed a damages action against various entities responsible for the design and manufacture of his plane’s ejection equipment. 8 During pretrial discovery in thаt litigation, two of the parties (respondents Weber 9 and Mills 10 ) sought discovery of all Air Force investigative reports pertaining to the accident. The Air Force released the entire record of the collateral investigation, as well as certain factual portions of the safety investigation, but it refused to release the confidential portions of the safety investigation.
Confidential statements made to air crash safety investigators wеre held to be privileged with respect to pretrial discovery over 20 years ago.
Machin
v.
Zukert,
114 U. S. App. D. C. 335,
In the District Court the Government filed an affidavit executed by the General responsible for Air Force safety investigations, explaining that the material that had been withheld
*797
contained “conclusions, speculations, findings and recommendations made by the Aircraft Mishap Investigators” as well as “testimony provided by witnesses under a pledge of confidentiality.” App. 38. The affidavit explained why the General believed that the national security would be adversely affected by the disclosure of such material.
11
The District Court held that the material at issue would not be available by law to a party other than an agency in litigation with an agency, and hence need not be disclosed by virtue of
*798
Exemption 5.
12
The Court of Appeals reversed.
► — I l-H
The plain language of the statute itself, as construed by our prior decisions, is sufficient to resolve the question presented. The statements of the two witnesses are unquestionably “intra-agency memorandums or letters” 13 and, since the Machín privilege normally protects them from discovery in civil litigation, they “would not be availаble by law to a party other than [the Air Force] in litigation with [the Air Force].” 14
*799
Last Term, in FTC v.
Grolier Inc.,
Grolier
was consistent with our prior cases. For example,
Grolier
itself relied on
Renegotiation Board
v.
Grumman Aircraft Engineering Corp.,
Respondents read
Merrill
as limiting the scope of Exemption 5 to privileges explicitly identified by Congress in the legislative history of the FOIA. But in
Merrill
we were confronted with a claimed exemption that was not clearly covered by a recognized pretrial discovery privilege. We held that Exemption 5 protected the Federal Open Market Committee’s Domestic Policy Directives although it was not entirely clear that they fell within any recognized civil discovery privilege because statements in the legislative history supported an inference that Congress intended to recognize such a privilege. See
Moreover, respondents’ contention that they can obtain through the FOIA material that is normally privileged would create an anomaly in that the FOIA could be used to supplement civil discovery. We have consistently rejected such a construction of the FOIA. See
Baldrige
v.
Shapiro,
Finally, the legislative history of Exemption 5 does not contain the kind of compеlling evidence of congressional intent that would be necessary to persuade us to look beyond the plain statutory language. Because of the difficulty inherent in compiling an exhaustive list of evidentiary privileges,
21
it would be impractical to treat the legislative history of Exemption 5 as containing a comprehensive list of all privileges Congress intended to adopt. Rather, the history of Exemption 5 can be understood by means of “rough analogies.”
EPA
v.
Mink, supra,
at 86. The legislative history of Exemption 5 indicates that Congress intended to incorporate governmental privileges analogous to the
Machín
privilege. That history recognizes a need for claims of privilege when confidentiality is necessary to ensure frank and open discussion and hence efficient governmental operations. See
Grolier,
*804 We therefore simply interpret Exemption 5 to mean what it says. The judgment of the Court of Appeals is
Reversed.
Notes
“On complaint, the district court of the United States in the district in which the complainant resides, or has his principal place of business, or in which the agency records are situated, оr in the District of Columbia, has jurisdiction to enjoin the agency from withholding agency records and to order the production of any agency records improperly withheld from the complainant. In such a case the court shall determine the matter de novo, and may examine the contents of such agency records in camera to determine whether such records or any part thereof shall be withheld under any of the exemptions set fоrth in subsection (b) of this section, and the burden is on the agency to sustain its action.” 5 U. S. C. § 552(a)(4)(B) (1982 ed.).
“This section does not apply to matters that are—
“(1) (A) specifically authorized under criteria established by an Executive order to be kept secret in the interest of national defense or foreign policy and (B) are in fact properly classified pursuant to such Executive order;
“(2) related solely to the internal personnel rules and practices of an agency;
“(3) specifically exempted from disclosure by statute (other than section 552b of this title), provided that such statute (A) requires that the matters be withheld from the public in such a manner as to leave no discretion on the issue, or (B) establishes particular criteria for withholding or refers to particular types of matters to be withheld;
“(4) trade secrets and commercial or financial information obtained from a person and privileged or confidential;
“(5) inter-agency or intra-agеncy memorandums or letters which would not be available by law to a party other than an agency in litigation with the agency;
“(6) personnel and medical files and similar files the disclosure of which would constitute a clearly unwarranted invasion of personal privacy;
“(7) investigatory records compiled for law enforcement purposes, but only to the extent that the production of such records would (A) interfere with enforcement proсeedings, (B) deprive a person of a right to a fair trial or an impartial adjudication, (C) constitute an unwarranted invasion of personal privacy, (D) disclose the identity of a confidential source and, in the case of a record compiled by a criminal law enforcement authority in the course of a criminal investigation, or by an agency conducting a lawful national security intelligence investigation, confidential information furnishеd only by the confidential source, (E) disclose investigative techniques and procedures, or (F) endanger the life or physical safety of law enforcement personnel;
“(8) contained in or related to examination, operating, or condition reports prepared by, on behalf of, or for the use of an agency responsible for the regulation or supervision of financial institutions; or
“(9) geological and geophysical informаtion and data, including maps, concerning wells.” 5 U. S. C. § 552(b) (1982 ed.).
Air Force Regulations 110-14, ¶ 1(a) (July 18, 1977).
Air Force Regulations 127-4, ¶ 19(a)(1) (Jan. 1, 1973).
Id., ¶3-8(d) (Jan. 18, 1980).
Id., ¶ 19(a)(3) (Jan. 1, 1973); id., ¶¶2-4, 2-5 (Jan. 18, 1980).
Id., ¶ 19(a)(4) (Jan. 1, 1973) states: “Notwithstanding the restrictions on use of these reports and their attachments and the prohibitions in this regulation against their release, factual material included in *796 accident/incident reports, covering examination of wreckage, photographs, plotting charts, wreckage diagrams, maps, transcripts of air traffic communications, weather reports, maintenancе records, crew qualifications, and like nonpersonal evidence may be released as required by law or pursuant to court order or upon specific authorization of The Judge Advocate General after consultation with The Inspector General. Also, Federal law requires that an accused in a trial by court-martial will, upon proper court order, be furnished all statements sworn or unsworn in any form which have been given to any Federal agent, employee, investigating officer, or board by any witness who testifies against the accused.”
Hoover v. Weber Aircraft Corp., No. CV 74-1064-WPG (CD Cal.).
Weber Aircraft Corp.
Mills Manufacturing Corp.
“[T];he release of the withheld portions of the Aircraft Mishap Investigation for litigation purposes would be harmful to our national security. The strength of the United States Air Force, upon which our national security is greatly dependent, is seriously affected by the number of major aircraft accidents which occur. The successful flight safety рrogram of the United States Air Force has contributed greatly to the continuously decreasing rate of such accidents. The effectiveness of this program depends to a large extent upon our ability to obtain full and candid information on the cause of each aircraft accident. Much of the information received from persons giving testimony in the course of an aircraft mishap investigation is conjecture, speculatiоn and opinion. Such full and frank disclosure is not only encouraged but is imperative to a successful flight safety program. Open and candid testimony is received because witnesses are promised that for the particular investigation their testimony will be used solely for the purpose of flight safety and will not be disclosed outside of the Air Force. Lacking authority to subpoena witnesses, accident investigators must rely on such assurances in order to оbtain full and frank discussion concerning all the circumstances surrounding an accident. Witnesses are encouraged to express personal criticisms concerning the accident.
“If aircraft mishap investigators were unable to give such assurances, or if it were felt that such promises were hollow, testimony and input from witnesses and from manufacturers; in many instances would be less than factual and a determination of the exact cause fаctors of accidents would be jeopardized. This would seriously hinder the accomplishment of prompt corrective action designed to preclude the occurrence of a similar accident. This privilege, properly accorded to the described portions of an United States Air Force Mishap Report of Investigation, including those portions reflecting the deliberations of the Investigating Board, is the very foundation of a successful Air Force flight safety program.” App. 38-39.
The District Court also held that a medical report sought by respondents was covered by Exemption 5, and that disclosure of both the report and the statements was inappropriate because in its view the public interest in maintaining confidentiality outweighed respondents’ interests in obtaining the material. The Court of Appeals rejected both of these holdings, and the Government does not sеek review on either.
Weber contends that “intra-agency memorandums or letters” cannot include statements made by civilians to Air Force personnel. Whatever the merits of this assertion, it is irrelevant to this case since the material at issue here includes only statements made by Air Force personnel.
Weber contends that the material at issue is not privileged because it was not obtained pursuant to a promise of confidentiality. Hоwever,
*799
the District Court found otherwise, and since that finding is supported by an uncontroverted affidavit submitted by the Government to the District Court, see
id.,
at 38, there is no basis for setting it aside. In all other respects, respondents concede that the requested material is covered by the
Machín
privilege, and did not file a cross-petition for certiorari challenging the Court of Appeals’ conclusion that the requested material was privileged. Thus, we assume without deciding that the material respondents seek is privileged, and do not consider the arguments of
amici
that no privilege is applicable here. See
United Parcel Service, Inc.
v.
Mitchell,
See also
See also
Respondents contend that
Mink
stands for the proposition that purely factual material can never qualify for protection under Exemption 5. However, thе relevant portion of
Mink
merely states that otherwise nonprivileged factual material cannot be withheld under Exemption 5 merely because it appears in the same document as privileged material, and that Congress intended to adopt the relevant case law on privilege. Moreover,
Mink
cited
Machín
with approval as part of that case law. See
Moreover, in the
Merrill
dictum we added: “We hesitate to construe Exemption 5 to incorporate a civil discovery privilege that would substantially duplicate another exemption.”
The regulation governing the Machín privilege also describes it as executive privilege. Air Force Regulations 127-4, ¶ 2-5 (Jan. 18, 1980).
Respondents also argue that their need for the requested material is great and that it would be unfair to expect them to defend the litigation brought against them by Captain Hoover without access to it. We answered this argument in
Grolier,
noting that the fact that in particular litigation a party’s particularized showing of need may on occasion justify discovery of privileged material in order to avoid unfairness does not mean that such material is routinely discoverable and hence outside the scope of Exemption 5. See
This difficulty is illustrated by the controversy surrounding the proposed provisions of the Federal Rules of Evidenсe governing privileges, which were rejected by Congress. See generally 2 J. Weinstein & M. Berger, Evidence ¶ 501[01] (1982).
Moreover, the Senate Report stated that Exemption 5 had been drafted in response to comments of federal agencies made in the course of Committee hearings, S. Rep. No. 813, at 4, 9. During those hearings, the Government submitted material indicating that the Machín privilege should be incorporated into the FOIA. See Administrative Procedure Act: Hearings before the Subcommittee on Administrative Practice and Procedure of the Senate Committee on the Judiciary, 89th Cong., 1st Sess., 196, 206, 366-367, 418 (1966).
“We agree with the Government that when disclosure of investigative reports obtained in large part through promises of confidentiality would hamper the efficient operation of an important Government program and perhaps even, as the Secretary here claims, impair the national security by weakening a branch of the military, the reports should be considered privileged.” 114 U. S. App. D. C., at 338,
It follows that recognition of the Machín privilege would not be inconsistent with the fundamental goals of the FOIA since it does not necessarily reduce the amount of information available to the public. The privilege is recognized because the Government would not be able to obtain the information but for its assurance of confidentiality. Thus, much if not all of the information covered by the Machín privilege would not find its way into the public realm even if we refused to recognize the privilege, since under those circumstances the information would not be obtained by the Government in the first place.
Cf.
Federal Open Market Committee
v.
Merrill,
Respondents rely on the fact that in recent years Congress has several times failed to act on proposed legislation which would have codified the Machín privilege. However, this does not represent a rejection of the privilege. To the contrary, Congress has enacted Federal Rule of Evidence 501, which recognizes the power of the courts to fashion common-law *804 rules of privilege. Congressional refusal to codify the Machín privilege hardly limits the power of courts to reсognize the privilege under Rule 501. Indeed, Rule 501 was adopted precisely because Congress wished to leave privilege questions to the courts rather than attempt to codify them. See H. R. Rep. No. 93-650, p. 8 (1973); S. Rep. No. 93-1277, pp. 11,13 (1974); supra, at 802-803, and n. 21. Congressional failure to codify this privilege is therefore irrelevant to our inquiry. Respondents also rely on legislation enacted after Exemption 5 concerning the scope of Exemption 3 and various other statutes. This legislation obviously sheds no light on the scope of Exemption 5.
