For any ship of the United States, other than a cargo ship of less than three hundred gross tons, to be navigated in the open sea outside of a harbor or port, or for any ship of the United States or any foreign country, other than a cargo ship of less than three hundred gross tons, to leave or attempt to leave any harbor or port of the United States for a voyage in the open sea, unless such ship is equipped with an efficient radio station in operating condition, as specified by subparagraphs (A) and (B) of this paragraph, in charge of and operated by one or more radio officers or operators, adequately installed and protected so as to insure proper operation, and so as not to endanger the ship and radio station as hereinafter provided, and, in the case of a ship of the United States, unless there is on board a valid station license issued in accordance with this chapter.