47 U.S.C. § 351: Ship radio stations and operations

Passenger ships irrespective of size and cargo ships of one thousand six hundred gross tons and upward shall be equipped with a radiotelegraph station complying with the provisions of this part; Cargo ships of three hundred gross tons and upward but less than one thousand six hundred gross tons, unless equipped with a radiotelegraph station complying with the provisions of this part, shall be equipped with a radiotelephone station complying with the provisions of this part. For any ship of the United States of one thousand six hundred gross tons and upward to be navigated in the open sea outside of a harbor or port, or for any such ship of the United States or any foreign country 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 efficient radio direction finding apparatus approved by the Commission, properly adjusted in operating condition as hereinafter provided. A ship which is not subject to the provisions of this part at the time of its departure on a voyage shall not become subject to such provisions on account of any deviation from its intended voyage due to stress of weather or any other cause over which neither the master, the owner, nor the charterer (if any) has control.