Code of Federal Regulations Title 27. Alcohol, Tobacco Products and Firearms § 27.28.21 General

(a) Vessels or aircraft operated by the United States;

(b) Vessels of the United States employed in the fisheries as provided in § 28.22 or in the whaling business, or actually engaged in foreign trade or trade between the Atlantic and Pacific ports of the United States or between the United States and any of its possessions, or between Hawaii and any other part of the United States or between Alaska and any other part of the United States;

(c) Aircraft registered in the United States and actually engaged in foreign trade or trade between the United States and any of its possessions, or between Hawaii and any other part of the United States or between Alaska and any other part of the United States;

(d) Vessels of war of any foreign nation;

(e) Foreign vessels employed in the fisheries as provided in § 28.22 or in the whaling business, or actually engaged in foreign trade or trade between the United States and any of its possessions, or between Hawaii and any other part of the United States or between Alaska and any other part of the United States;  where such trade by foreign vessels is permitted;  or

(f) Aircraft registered in any foreign country and actually engaged in foreign trade or trade between the United States and any of its possessions, or between Hawaii and any other part of the United States or between Alaska and any other part of the United States, where trade by foreign aircraft is permitted, and where the Secretary of the Treasury shall have been advised by the Secretary of Commerce that he has found such foreign country allows, or will allow, substantially reciprocal privileges in respect to aircraft registered in the United States.