delivered the opinion of the Court.
Sunal and Kulick registered under the Selective Training and Service Act of 1940, 54 Stat. 885, 57 Stat. 597, 50 U. S. C. App. § 301, et seq. Each is a Jehovah’s Witness and each claimed the exemption granted by Congress to regular or duly ordained ministers of religion.1 § 5 (d). The local boards, after proceedings unnecessary to relate here, denied the claimed exemptions and classified these registrants as I-A. They exhausted their administrative remedies but were unable to effect a change in their classi*176fications. Thereafter they were ordered to report for induction — Sunal on October 25, 1944, Kulick on November 9, 1944. Each reported but refused to submit to induction. Each was thereupon indicted, tried and convicted under § 11 of the Act for refusing to submit to induction. Sunal was sentenced on March 22, 1945, Kulick on May 7, 1945, each to imprisonment for a term of years. Neither appealed.
At the trial each offered evidence to show that his selective service classification was invalid. The trial courts held, however, that such evidence was inadmissible, that the classification was final and not open to attack in the criminal trial. On February 4, 1946, we decided Estep v. United States and Smith v. United States, 327 U. S. 114. These cases2 held on comparable facts that a registrant, who had exhausted his administrative remedies and thus obviated the rule of Falbo v. United States, 320 U. S. 549, was entitled, when tried under § 11, to defend on the ground that his local board exceeded its jurisdiction in making the classification — for example, that it had no basis in fact. 327 U. S. pp. 122-123.
It is plain, therefore, that the trial courts erred in denying Sunal and Kulick the defense which they tendered. Shortly after the Estep and Smith cases were decided, petitions for writs of habeas corpus were filed on behalf of Sunal and Kulick. In each case it was held that habeas corpus was an available remedy. In Sunal’s case the Circuit Court of Appeals for the Fourth Circuit held that there was a basis in fact for the classification and affirmed a judgment discharging the writ. 157 F. 2d 165. *177In Kulick’s case the Circuit Court of Appeals for the Second Circuit reversed a District Court holding that there was evidence to support the classification, 66 F. Supp. 183, and ruled, without examining the evidence, that since Kulick had been deprived of the defense he should be discharged from custody without prejudice to further prosecution. 157 F. 2d 811. The cases are here on petitions for writs of certiorari, which we granted because of the importance of the questions presented.
The normal and customary method of correcting errors of the trial is by appeal. Appeals could have been taken in these cases,3 but they were not. It cannot be said that absence of counsel made the appeals unavailable as a practical matter. See Johnson v. Zerbst, 304 U. S. 458, 467. Defendants had counsel. Nor was there any other barrier to the perfection of their appeals. Cf. Cochran v. Kansas, 316 U. S. 255. Moreover, this is not a situation where the facts relied on were dehors the record and therefore not open to consideration and review on appeal. See Waley v. Johnston, 316 U. S. 101, 104; United States ex rel. McCann v. Adams, 320 U. S. 220, 221. And see Adams v. United States ex rel. McCann, 317 U. S. 269, 274-275. The error was of record in each case. It is said, however, that the failure to appeal was excusable, since under the decisions as they then stood — March 22, 1945, and May 7, 1945— the lower courts had consistently ruled that the selective service classification could not be attacked in a prosecution under § 11. See Estep v. United States, supra, p. 123, n. 15. It is also pointed out that on April 30, 1945, we had denied certiorari in a case which sought to raise the same *178point,4 and that Estep v. United States, supra, and Smith v. United States, supra, were brought here5 and decided after Sunal’s and Kulick’s time for appeal had passed. The argument is that since the state of the law made the appeals seem futile, it would be unfair to those registrants to conclude them by their failure to appeal.
We put to one side comparable problems respecting the use of habeas corpus in the federal courts to challenge convictions obtained in the state courts. See New York v. Eno, 155 U. S. 89; Tinsley v. Anderson, 171 U. S. 101, 104-105; United States ex rel. Kennedy v. Tyler, 269 U. S. 13; Ex parte Hawk, 321 U. S. 114, 116-117. So far as convictions obtained in the federal courts are concerned, the general rule is that the writ of habeas corpus will not be allowed to do service for an appeal. Adams v. United States ex rel. McCann, supra, p. 274. There have been, however, some exceptions. That is to say, the writ has at times been entertained either without consideration of the adequacy of relief by the appellate route or where an appeal would have afforded an adequate remedy. Illustrative are those instances where the conviction was under a federal statute alleged to be unconstitutional,6 where there was a conviction by a federal court whose jurisdiction over the person or the offense was challenged,7 where the trial or sentence by a federal court vio*179lated specific constitutional guaranties.8 It is plain, however, that the writ is not designed for collateral review of errors of law committed by the trial court — the existence of any evidence to support the conviction,9 irregularities in the grand jury procedure,10 departure from a statutory grant of time in which to prepare for trial,11 and other errors in trial procedure which do not cross the jurisdictional line. Cf. Craig v. Hecht, 263 U. S. 255.
Yet the latter rule is not an absolute one; and the situations in which habeas corpus has done service for an appeal are the exceptions. Thus where the jurisdiction of the federal court which tried the case is challenged or where the constitutionality of the federal statute under which conviction was had is attacked, habeas corpus is increasingly denied in case an appellate procedure was available for correction of the error.12 Yet, on the other hand, where the error was flagrant and there was no other remedy available for its correction, relief by habeas corpus has sometimes been granted.13 As stated by Chief Jus*180tice Hughes in Bowen v. Johnston, 306 U. S. 19, 27, the rule which requires resort to appellate procedure for the correction of errors “is not one defining power but one which relates to the appropriate exercise of power.” That rule is, therefore, “not so inflexible that it may not yield to exceptional circumstances where the need for the remedy afforded by the writ of habeas corpus is apparent.” Id. p. 27. That case was deemed to involve “exceptional circumstances” by reason of the fact that it indicated “a conflict between state and federal authorities on a question of law involving concerns of large importance affecting their respective jurisdictions.” Id. p. 27. The Court accordingly entertained the writ to examine into the jurisdiction of the court to render the judgment of conviction.
The same course was followed in Ex parte Hudgings, 249 U. S. 378, where petitioner was adjudged guilty of contempt for committing perjury. The Court did not require the petitioner to pursue any appellate route but issued an original writ and discharged him, holding that perjury without more was not punishable as a contempt. That situation was deemed exceptional in view of “the nature of the case, of the relation which the question which it involves bears generally to the power and duty of courts in the performance of their functions, of the dangerous effect on the liberty of the citizen when called upon as a witness in a court which might result if the erroneous doctrine upon which the order under review was based were not promptly corrected ....’’ Id. p. 384. Cf. Craig v. Hecht, supra.
The Circuit Courts of Appeals thought that the facts of the present cases likewise presented exceptional cir*181cumstances which justified resort to habeas corpus though no appeals were taken. In their view the failure to appeal was excusable, since relief by that route seemed quite futile.
But denial of certiorari by this Court in the earlier case imported no expression of opinion on the merits. House v. Mayo, 324 U. S. 42, 48, and cases cited. The same chief counsel represented the defendants in the present cases and those in the Estep and Smith cases. At the time these defendants were convicted the Estep and Smith cases were pending before the appellate courts. The petition in the Smith case was, indeed, filed here about two weeks before Kulick’s conviction and about a month after Sunal’s conviction. The same road was open to Sunal and Kulick as the one Smith and Estep took. Why the legal strategy counseled taking appeals in the Smith and Estep cases and not in these we do not know. Perhaps it was based on the facts of these two cases. For the question of law had not been decided by the Court; and counsel was pressing for a decision here. The case, therefore, is not one where the law was changed after the time for appeal had expired. Cf. Warring v. Colpoys, 122 F. 2d 642. It is rather a situation where at the time of the convictions the definitive ruling on the question of law had not crystallized. Of course, if Sunal and Kulick had pursued the appellate course and failed, their cases would be quite different. But since they chose not to pursue the remedy which they had, we do not think they should now be allowed to justify their failure by saying they deemed any appeal futile.
We are dealing here with a problem which has radiations far beyond the present cases. The courts which tried the defendants had jurisdiction over their persons and over the offense. They committed an error of law in excluding the defense which was tendered. That error did not go to the jurisdiction of the trial court. Congress, *182moreover, has provided a regular, orderly method for correction of all such errors by granting an appeal to the Circuit Court of Appeals and by vesting us with certiorari jurisdiction. It is not uncommon after a trial is ended and the time for appeal has passed to discover that a shift in the law or the impact of a new decision has given increased relevance to a point made at the trial but not pursued on appeal. Cf. Warring v. Colpoys, supra. If in such circumstances, habeas corpus could be used to correct the error, the writ would become a delayed motion for a new trial, renewed from time to time as the legal climate changed. Error which was not deemed sufficiently adequate to warrant an appeal would acquire new implications. Every error is potentially reversible error; and many rulings of the trial court spell the difference between conviction and acquittal. If defendants who accept the judgment of conviction and do not appeal can later renew their attack on the judgment by habeas corpus, litigation in these criminal cases will be interminable. Wise judicial administration of the federal courts counsels against such course, at least where the error does not trench on any constitutional rights of defendants nor involve the jurisdiction of the trial court.
An endeavor is made to magnify the error in these trials to constitutional proportions by asserting that the refusal of the proffered evidence robbed the trial of vitality by depriving defendants of their only real defense. But as much might be said of many rulings during a criminal trial. Defendants received throughout an opportunity to be heard and enjoyed all procedural guaranties granted by the Constitution. Error in ruling on the question of law did not infect the trial with lack of procedural due process. As stated by Mr. Justice Cardozo in Escoe v. Zerbst, 295 U. S. 490, 494, “When a hearing is allowed but there is error in conducting it or in limiting its scope, the remedy is by appeal. *183When an opportunity to be heard is denied altogether, the ensuing mandate of the court is void, and the prisoner confined thereunder may have recourse to habeas corpus to put an end to the restraint.”
It is said that the contrary position was indicated by the following statement in Estep v. United States, supra, pp. 124-125,
“But if we now hold that a registrant could not defend at his trial on the ground that the local board had no jurisdiction in the premises, it would seem that the way would then be open to him to challenge the jurisdiction of the local board after conviction by habeas corpus. The court would then be sending men to jail today when it was apparent that they would have to be released tomorrow.”
We were there examining the alternative pressed on us— that the classification could not be attacked at the trial. If we denied the defense, we concluded that habeas corpus would lie the moment after conviction.' For one convicted of violating an illegal order of a selective service board, like one convicted of violating an unconstitutional statute, should be afforded an opportunity at some stage to establish the fact. And where no other opportunity existed, habeas corpus would be the appropriate remedy.14 But that was an additional reason for allowing the defense in the criminal trial, not a statement that defendants prosecuted under § 11 had an alternative of'defending at the trial on the basis of an illegal classification or resorting to habeas corpus after conviction. These registrants had available a method of obtaining the right to defend their prosecutions under § 11 on that ground. They did not use *184it. And since we find no exceptional circumstances which excuse their failure, habeas corpus may not now be used as a substitute.
Accordingly Sunal v. Large will be affirmed and Alexander v. Kulick will be reversed.
So ordered.
Mr. Justice Burton concurs in the result.Sunal in 1942 was classified as a conscientious objector and ordered to report for work of national importance. On his failure to do so he was convicted under the Act and a fine and term of imprisonment were imposed. The events with which we are now concerned relate to his classification after his discharge from prison.
The Smith case was decided by the Circuit Court of Appeals on April 4, 1945, 148 F. 2d 288; the petition for certiorari was filed April 25, 1945, and granted May 28, 1945. 325 U. S. 846. The Estep case was decided by the Circuit Court of Appeals on July 6, 1945, 150 F. 2d 768; the petition for certiorari was filed August 3, 1945, and granted October 8, 1945. 326 U. S. 703.
We therefore lay to one side cases such as Bridges v. Wixon, 326 U. S. 135, Duncan v. Kahanamoku, 327 U. S. 304, and Eagles v. United States ex rel. Samuels, 329 U. S. 304, where the order of the agency under which petitioner was detained was not subject to judicial review.
Rinko v. United States, 325 U. S. 851. We also denied certiorari in Flakowicz v. United States, 325 U. S. 851; but it, like Falbo v. United States, supra, was one where the administrative remedies had not been exhausted, there being an additional examination which the registrant had not taken. See Gibson v. United States, 329 U. S. 338.
See note 2, supra.
Ex parte Siebold, 100 U. S. 371; Ex parte Curtis, 106 U. S. 371; Ex parte Yarbrough, 110 U. S. 651; In re Coy, 127 U. S. 731; Matter of Heff, 197 U. S. 488; Matter of Gregory, 219 U. S. 210; Baender v. Barnett, 255 U. S. 224.
Ex parte Watkins, 3 Pet. 193; Ex parte Parks, 93 U. S. 18; Bowen v. Johnston, 306 U. S. 19.
Ex parte Lange, 18 Wall. 163 (double jeopardy); In re Snow, 120 U. S. 274 (same); In re Nielsen, 131 U. S. 176 (same); Counselman v. Hitchcock, 142 U. S. 547 (self-incrimination); Ex parte Wilson, 114 U. S. 417 (requirement of indictment); Ex parte Bain, 121 U. S. 1 (same); Callan v. Wilson, 127 U. S. 540 (jury trial); Johnson v. Zerbst, supra (right to counsel); Walker v. Johnston, 312 U. S. 275 (same); Waley v. Johnston, supra (coerced plea of guilty).
Harlan v. McGourin, 218 U. S. 442.
Ex parte Harding, 120 U. S. 782; Kaizo v. Henry, 211 U. S. 146.
McMicking v. Schields, 238 U. S. 99. The rule is even more strict where habeas corpus is sought before trial. See Johnson v. Hoy, 227 U. S. 245.
In re Lincoln, 202 U. S. 178; Toy Toy v. Hopkins, 212 U. S. 542; Glasgow v. Moyer, 225 U. S. 420.
Tinsley v. Treat, 205 U. S. 20 (removal case). In removal cases habeas corpus is available not to weigh the evidence to support the accusation but to determine whether there is an entire lack of evidence to support it. Hyde v. Shine, 199 U. S. 62, 84. It is also available to determine whether removal to the district in question violates a constitutional right of the accused, Haas v. Henkel, 216 U. S. 462, or *180whether the court before which it is proposed to take and try the accused has jurisdiction over the offense. Salinger v. Loisel, 265 U. S. 224. But habeas corpus will not be entertained to pass on the question of jurisdiction where it involves consideration of many facts and seriously controverted questions of law. Rodman v. Pothier; 264 U. S. 399; Henry v. Henkel, 235 U. S. 219.
The remedy of habeas corpus extends to a ease where a person “is in custody in violation of the Constitution or of a law ... of the United States ...” R. S. § 753,28 U. S. C. § 453.