19 CFR §4.21

1. (a)Tonnage taxes and light money shall be suspended in whole or in part whenever the President by proclamation shall so direct.
2. (b)The following vessels, or vessels arriving in the circumstances as defined below, shall be exempt from tonnage tax and light money:
   1. (1)It comes into port for bunkers (including water), sea stores, or ship's stores; transacts no other business in the port; and departs within 24 hours after its arrival.
   2. (2)It arrives in distress, even though required to enter.
   3. (3)It is brought into port by orders of United States naval authorities and transacts no business while in port other than the taking on of bunkers, sea stores, or ship's stores.
   4. (4)It is a vessel of war or other vessel which is owned by, or under the complete control and management of the United States or the government of a foreign country, and which is not carrying passengers or merchandise in trade or, if in ballast, which is not arriving from a foreign port during the usual course of its employment as a vessel engaged in trade.
   5. (5)It is a yacht or other pleasure vessel not carrying passengers or merchandise in trade.
   6. (6)It is engaged exclusively in scientific activities.
   7. (7)It is engaged exclusively in laying or repairing cables.
   8. (8)It is engaged in whaling or other fisheries, even though it may have entered a foreign port for fuel or supplies, if it did not carry passengers or merchandise in trade.
   9. (9)It is a passenger vessel making three trips or more a week between a port of the United States and a foreign port.
   10. (10)It is used exclusively as a ferry boat, including a car ferry.
   11. (11)It enters otherwise than by sea from a foreign port at which tonnage or lighthouse duties or equivalent taxes are not imposed on vessels of the United States (applicable only where the vessel arrives from a port in the province of Ontario, Canada).
   12. (12)It is a coastwise-qualified vessel solely engaged in the coastwise trade (although arriving from a foreign port or place, it is engaged in the transportation of merchandise or passengers, or the towing of a vessel other than a vessel in distress, between points in the U.S. via a foreign point) (see §§ 4.80, 4.80a, 4.80b, and 4.92).
   13. (13)It is a vessel entering directly from the Virgin Islands (U.S.), American Samoa, the islands of Guam, Wake, Midway, Canton, or Kingman Reef, or Guantanamo Bay Naval Station.
   14. (14)It is a vessel making regular daily trips between any port of the United States and any port in Canada wholly upon interior waters not navigable to the ocean, except that such a vessel shall pay tonnage taxes upon her first arrival in each calendar year.
   15. (15)It is a vessel arriving at a port in the United States which, while proceeding between ports in the United States, touched at a foreign port under circumstances which would have exempted it from making entry under section 441(4), Tariff Act of 1930, as amended (19 U.S.C. 1441(4)), had it touched at a United States port.