10 U.S. Code § 774. Religious apparel: wearing while in uniform
(b)Exceptions.—The Secretary concerned may prohibit the wearing of an item of religious apparel—
in circumstances with respect to which the Secretary determines that the wearing of the item would interfere with the performance of the member’s military duties; or
(d)Religious Apparel Defined.—
In this section, the term “religious apparel” means apparel the wearing of which is part of the observance of the religious faith practiced by the member.