((a)) ** General rule** There is hereby imposed a tax on any port use.

((b)) ** Amount of tax** The amount of the tax imposed by subsection (a) on any port use shall be an amount equal to 0.125 percent of the value of the commercial cargo involved.

((c)) ** Liability and time of imposition of tax**

((1)) ** Liability** The tax imposed by subsection (a) shall be paid by—

((A)) in the case of cargo entering the United States, the importer, or

((B)) in any other case, the shipper.

((2)) ** Time of imposition** Except as provided by regulations, the tax imposed by subsection (a) shall be imposed at the time of unloading.