Section, act Aug. 10, 1956, ch. 1041, 70A Stat. 503; Pub. L. 87–143, § 1(2), Aug. 17, 1961, 75 Stat. 364; Pub. L. 90–235, § 2(a)(4)(A), Jan. 2, 1968, 81 Stat. 756; Pub. L. 96–513, title V, § 514(2), Dec. 12, 1980, 94 Stat. 2935, provided that, in peace time, Air Force enlistment was available only to citizens and persons lawfully admitted to the United States for permanent residence.