A Selective Service draft board classified Jack McKart (defendant) as exempt from military service under the Selective Service Act of 1948 (Act), 50 U.S.C. § 456(o), which provided an exemption for sole surviving sons of veterans who had been killed in action. The draft board later incorrectly reclassified McKart as immediately eligible to serve, and ordered McKart to report for a medical exam as part of his induction. Because McKart objected to the Vietnam War, he declined to appeal his reclassification to a state appeal board (board). At the time McKart was reclassified, draft registrants were not required to appeal their classifications to the board. After McKart failed to appear for his scheduled medical exam, he was federally charged and indicted for failing to report for service. McKart attempted to argue that he was exempt from service because his original classification had been correct. The district court ruled that McKart could not assert the exemption defense, because he had failed to exhaust his administrative remedies. McKart was convicted and sentenced to three years in prison. The court of appeals affirmed. The United States Supreme Court granted certiorari.