MR. JUSTICE WHITE delivered the opinion of the Court.Congress has provided in 10 U.S.C. § 687(a) [Footnote 1] that an otherwise eligible member of a reserve component of the Armed Forces, who is involuntarily released from active duty,"and who has completed, immediately before his release, at least five years of continuous active duty, is entitled to a readjustment payment computed by multiplying his years of active service . . . by two months' basic pay of the grade in which he is serving at the time of his release."It is further provided that"[f]or the purposes of this subsection -- . . .(2) a part of a year that is six Page 417 U. S. 74 months or more is counted as a whole year, and a part of a year that is less than six months is disregarded. . . ."We must decide whether the "rounding" provision set forth in § 687(a)(2) is to be applied in determining eligibility for readjustment pay, as well as in computing the amount of readjustment pay to which an eligible reservist is entitled, so that involuntarily released reservists who have completed four years and six months or more, but less than five years, of continuous active duty prior to their release are nonetheless entitled to a readjustment payment.  The Court of Appeals held that the rounding clause applied only to computation of readjustment payments, 483 F.2d 220 (CA9 1973), contrary to the earlier decision of the Court of Claims that the rounding provision is applicable in determining eligibility for, as well as computation of, readjustment payments under § 687.  Schmid v. United States, 193 Ct.Cl. 780, 436 F.2d 987, cert. denied, 404 U.S. 951 (1971).  We granted certiorari to resolve the conflict, 414 U.S. 1128 (1974), and now affirm the judgment of the Court of Appeals.Each petitioner had served continuously for more than four years and six months, but less than five years, when notified that he would be honorably but involuntarily released from active duty in the Reserves.  In No. 73-604, petitioner Cass, a captain in the Army Reserve, was, in fact, released from active duty before completing five Page 417 U. S. 75 years of service, and when the Army denied his request for readjustment pay, he brought suit in the United States District Court for the District of Montana, which granted relief on the authority of the Court of Claims' decision in Schmid, supra.  In No. 73-5661, petitioners Adams, Steneman, and Youngquist, captains in the Marine Corps Reserve, brought separate actions in the Central District of California, prior to their release, seeking a modification of their release orders to provide for readjustment pay.  The District Court subsequently held that they were entitled to readjustment pay based on active service of more than four and one-half years. [Footnote 2]  The Government's appeals from the decisions of the two District Courts were consolidated, and the Court of Appeals reversed each, holding that the statute and its legislative history make clear that readjustment pay is not to be provided to reservists involuntarily released from active duty with less than five full years of continuous service. [Footnote 3]Petitioners assert to the contrary that the language of § 687(a) unambiguously establishes that four and Page 417 U. S. 76 one-half years of continuous active service qualifies a involuntarily released reservist for readjustment benefits, that the legislative history of the rounding provision should therefore not be considered in resolving the issue, and that, even if the legislative history is considered, it supports the construction urged by petitioners as much as that contended for by the Government.  We are unpersuaded by these arguments, however.The statute sets out both the eligibility requirements for entitlement to readjustment pay and the method of computing the amount of the applicable payment in the same sentence.  Entitlement is based, in part, on the completion, immediately before the involuntary release of a reservist, of "at least five years of continuous active duty," and the payment is to be computed by multiplying the reservist's "years of active service" by two months' basic pay of the grade in which he is serving when released.  Because the rounding provision expressly provides that it is to be applied for "purposes of this subsection," petitioners contend that the provision modifies the term "year" whenever that term appears in the subsection, i.e., to determine whether a reservist has completed five years of service to be eligible for readjustment benefits, as well as to determine the number of years of service to use as a multiplier in computing the amount of readjustment pay owed.  This is so plainly true, petitioners contend, that resort to legislative history is unnecessary and improper. [Footnote 4] Page 417 U. S. 77Our view is to the contrary.  The rounding provision is arguably subject to the interpretation given it by petitioners, but did Congress intend that provision to override its explicit requirement of "at least" five years of service?  We think the answer to that question is sufficiently doubtful to warrant our resort to extrinsic aids to determine the intent of Congress, which, of course, is the controlling consideration in resolving the issue before us. [Footnote 5]  Moreover, Page 417 U. S. 78 the Court has previously stated that"[w]hen aid to construction of the meaning of words, as used in the statute, is available, there certainly can be no 'rule of law' which Page 417 U. S. 79 forbids its use, however clear the words may appear on 'superficial examination,'"United States v. American Trucking Assns., Inc., 310 U. S. 534,  310 U. S. 543-544 (1940); Harrison v. Northern Trust Co., 317 U. S. 476,  317 U. S. 479 (1943).  Such aid is available in this case and we decline to ignore the clearly relevant history of § 687(a).Certain reservists involuntarily released from active duty are granted lump-sum readjustment pay to help them readjust to civilian life and to encourage qualified reservists to remain on active duty for extended periods.  Readjustment pay was first provided by the Act of July 9, 1956, 70 Stat. 517, which conditioned entitlement on the completion immediately prior to release of "at least five years of continuous active duty."  It also provided that,"[f]or the purposes of computing the amount of readjustment payment (1) a part of a year that is six months or more is counted as a whole year, and a part of a year that is less than six months is disregarded. . . ."Ibid.  As first introduced and passed by the House, however, the bill provided, as the codified version does now, that "[f]or the purposes of this subsection," the six-month rounding provision would apply.  H.R.Rep. No.1960, 84th Cong., 2d Sess., 9 (1956); 102 Cong.Rec. 10120 (June 12, 1956).  It was nonetheless made clear by the debate in the House prior to passage that five years was to be the minimum eligibility requirement. [Footnote 6]  Page 417 U. S. 80 The Senate, focusing on a letter from the Comptroller General to the Chairman of the Armed Services Committee suggesting that the language be clarified to ensure that five years was to be the minimum period necessary to qualify for a readjustment payment, amended the bill to reflect this more clearly, [Footnote 7] id. at 11333-11334 Page 417 U. S. 81 (June 29, 1956), and the House readily concurred the same day in the Senate amendments to the bill as the final language of the 1956 Act, id. at 11503-11504.The Act was amended in June, 1962, primarily to raise the amount of readjustment benefits paid to involuntarily released reservists to equal the amount provided as severance pay to involuntarily released regular officers, [Footnote 8] but it retained the explicit language specifying the use of the rounding provision for "purposes of computing the amount of the readjustment payment," 76 Stat. 120, and there was no discussion in the congressional reports [Footnote 9] suggesting any modification of this language.  Less than three months later, however, the present language was adopted as part of a measure codifying "recent military laws."  Act of Sept. 7, 1962, 76 Stat. 506.  The committee reports accompanying the codification proposal make plain that no change in the eligibility requirements for readjustment pay was intended by the enacted change in phraseology. [Footnote 10]  The Senate Judiciary Committee Report explained the purpose of the proposal as follows:"This bill, as amended, is not intended to make any substantive change in existing law. Its purpose is to bring up to date title 10 of the United States Code, by incorporating the provisions of a number of public laws that were passed while the bill to enact title 10 into law was still pending in the Congress, and to transfer to title 10 provisions now in Page 417 U. S. 82 other parts of the code."S.Rep. No. 1876, 87th Cong., 2d Sess., 6 (1962).  The same limited purpose was expressed by the House Judiciary Committee, which further explained that"[s]ome changes in style and form have been made to conform the provisions to the style and form of title 10, but these changes do not affect the substance."H.R.Rep. No. 1401, 87th Cong., 2d Sess., 1 (1962).These congressional comments, combined with the fact that no consideration of any change in eligibility standards appears in either the cited committee reports or in the proceedings leading to adoption of the codification bill by the House, 108 Cong.Rec. 4435-4441 (1962), and by the Senate. 108 Cong.Rec. 17088-17089 (1962), conclusively demonstrate that Congress did not reduce the minimum period of qualifying service for entitlement to readjustment benefits from five to four and one-half years when it substituted the words in the codified version of § 687(a) for the unambiguous language of the prior substantive enactments.  We are unpersuaded by petitioners' claim that the codified version is nevertheless to be accepted as correctly expressing the will of Congress and as a mere unexplained version of the language of prior law, see Continental Casualty Co. v. United States, 314 U. S. 527,  314 U. S. 529-530 (1942); United States v. Bowen, 100 U. S. 508,  100 U. S. 513 (1880).  Here, the meaning of the predecessor statute is clear, and quite different from the meaning petitioners would ascribe to the codified law; and the revisers expressly stated that changes in language resulting from the codification were to have no substantive effect.  Fourco lass Co. v. Transmirra Products Corp., 353 U. S. 222,  353 U. S. 227-228 (1957); United States v. Cook, 384 U. S. 257,  384 U. S. 260 (1966); City of Greenwood v. Peacock, 384 U. S. 808,  384 U. S. 815-816 (1966). Page 417 U. S. 83The Court of Claims in the Schmid case, 193 Ct.Cl. 780, 436 F.2d 987 (1971), thought that, in codifying 687(a), Congress restored the original language of the 1956 House bill, which it knew had been interpreted by the Comptroller General as reducing the minimum eligibility requirement to four years, six months.  Id. at 787, 436 F.2d  at 991.  But the codification language was accompanied by no reference to the 1956 legislation or to the views then expressed by the Comptroller General. [Footnote 11]  What is more, it is plain that the language of the original 1956 bill was itself not intended to set the minimum eligibility period at less than five years. [Footnote 12] The codification, if construed as petitioners would have it, would not represent a "return" to the original intent of Congress.  It is also significant that there is no hint of any consideration of what such a change would cost or how it would affect the goals of the readjustment pay provisions, contrary to the careful attention these matters received when benefits under the readjustment pay statute were raised in 1962.  As Judge Nichols commented in dissenting from the decision in Schmid:  "In resolving ambiguity, we must allow ourselves some recognition of the existence of sheer inadvertence in the legislative process."  Id. at 789, 436 F.2d  at 992.  Finally, we cannot agree with the contention that a change in minimum eligibility from five to four and one-half years should not be considered a "substantive change" because, once a reservist must reenlist beyond the initial enlistment term of four years, the purpose of the readjustment benefit scheme as an inducement to extended service is satisfied.  Not only is the selection of the particular minimum term of eligibility a peculiarly legislative task dependent upon substantive judgment, but the very fact that such a Page 417 U. S. 84 change involves a substantially greater expenditure of funds places this sort of revision into the substantive realm.We thus conclude that the rounding provision of § 687(a)(2) is applicable only in the determination of how much readjustment pay an otherwise qualified reservist is authorized, and that such a reservist must serve a minimum of five full years of continuous active duty before he is involuntarily released in order to be eligible for readjustment benefits.  The judgment of the Court of Appeals isAffirmed
U.S. Supreme CourtCass v. United States, 417 U.S. 72 (1974)Cass v. United StatesNo. 73-604Argued April 16, 1974Decided May 28, 1974*417 U.S. 72SyllabusTitle 10 U.S.C. § 687(a) provides for readjustment pay for an Armed Forces reservist who is involuntarily released from active duty and has completed, immediately before his release, "at least five years of continuous active duty," computed by multiplying his years of active service by two months' basic pay of his grade at the time of release, and further provides that"[f]or the purposes of this subsection -- . . . (2) a part of a year that is six months or more is counted as a whole year, and a part of a year that is less than six months is disregarded. . . ."Held:  The "rounding" provision, as is clear from the statute's legislative history, applies only in computing the amount of readjustment pay, and not in determining eligibility therefor; hence, a reservist must serve a minimum of five full years of continuous active duty before his involuntary release in order to qualify for readjustment benefits.  Pp.  417 U. S. 75-84.483 F.2d 220, affirmed.WHITE, J., delivered the opinion of the Court, in which BURGER, C.J., and BRENNAN, STEWART, MARSHALL, BLACKMUN, POWELL, and REHNQUIST, JJ., joined.  DOUGLAS, J., filed a dissenting statement, post, p.  417 U. S. 84. Page 417 U. S. 73