IP-X8 submersible, plug-and-play connectivity, controls all function (including DSC) of Icom's IC-M504A or IC-M604A VHF marine radios. Large LCD with adjustable lighting level. Doubles as an intercom. IC-M604A accepts up to 2 COMMANDMICIIIs. It's like getting a second (or third) on-board radio station for the cost of an accessory. Instructions for using the COMMANDMICIII are included as part of the IC-M504A and IC-M604A instruction manuals.