On the exportation of beer, brewed or produced in the United States, the brewer thereof shall be allowed a drawback equal in amount to the tax paid on such beer if there is such proof of exportation as the Secretary may by regulations require. For the purpose of this section, exportation shall include delivery for use as supplies on the vessels and aircraft described in section 309 of the Tariff Act of 1930, as amended (19 U.S.C. 1309).