19 CFR § 12.98 - Importations permitted by statutory exceptions.
The importation of switchblade knives is permitted by 15 U.S.C. 1244, when:
(a) Imported pursuant to contract with a branch of the Armed Forces of the United States;
(b) Imported by a branch of the Armed Forces of the United States or any member or employee thereof acting in the performance of his duty; or
(c) A switchblade knife, other than a ballistic knife, having a blade not exceeding 3 inches in length is in the possession of and is being transported on the person of an individual who has only one arm.