employment
For purposes of this chapter, the term “employment” means any service performed prior to 1955, which was employment for purposes of subchapter C of chapter 9 of the Internal Revenue Code of 1939 under the law applicable to the period in which such service was performed, and (A) any service, of whatever nature, performed after 1954 by an employee for the person employing him, irrespective of the citizenship or residence of either, (i) within the United States, or (ii) on or in connection with an American vessel or American aircraft under a contract of service which is entered into within the United States or during the performance of which and while the employee is employed on the vessel or aircraft it touches at a port in the United States, if the employee is employed on and in connection with such vessel or aircraft when outside the United States, and (B) any service, of whatever nature, performed after 1971 outside the United States (except in a contiguous country with which the United States has an agreement relating to unemployment compensation) by a citizen of the United States as an employee of an American employer (as defined in subsection (j)(3)), except—