47 U.S.C. § 354a

Cargo ships of three hundred gross tons and upward but less than one thousand six hundred gross tons may, in lieu of the radiotelegraph station prescribed by section 354 of this title , be equipped with a radiotelephone station complying with the following requirements: (a) The radiotelephone station shall be in the upper part of the ship, so located that it is sheltered to the greatest possible extent from noise which might impair the correct reception of messages and signals, and, unless such station is situated on the bridge, there shall be efficient communication with the bridge. (b) The radiotelephone installation shall be capable of transmitting and receiving on the frequencies, and using the classes of emission, designated by the Commission pursuant to law for the purposes of distress and safety of navigation. (c) The radiotelephone installation shall have a minimum normal range of one hundred and fifty nautical miles; that is, it shall be capable of transmitting and receiving clearly perceptible signals from ship to ship by day and under normal conditions and circumstances over this range. (d) There shall be available at all times a main source of electrical energy sufficient to operate the installation over the normal range required by subsection (c) of this section. If batteries are provided they shall have sufficient capacity to operate the transmitter and receiver for at least six continuous hours under normal working conditions. In installations made on or after November 19, 1952 , a reserve source of electrical energy shall be provided in the upper part of the ship unless the main source of energy is so situated.