26 CFR 31.3306(m)-1 - American vessel and aircraft.
(a) The term “American vessel” means any vessel which is documented (that is, registered, enrolled, or licensed) or numbered in conformity with the laws of the United States. It also includes any vessel which is neither documented nor numbered under the laws of the United States, nor documented under the laws of any foreign country, if the crew of such vessel is employed solely by one or more citizens or residents of the United States or corporations organized under the laws of the United States or of any State. (For provisions relating to the terms “State” and “citizen”, see § 31.3306(j)-1.)
(b) The term “American aircraft” means any aircraft registered under the laws of the United States.
(c) For provisions relating to services performed outside the United States on or in connection with an American vessel or American aircraft, see paragraph (c) of § 31.3306(c)-2.