This equipment utilizes the ship’s power supply of 24 volts DC to activate the voice communication circuits. With a press of the quick access button, you can communicate with the opposite party. 1. Marine Common Battery Telephones (Direct) 1) 1:1 Communication system: This system is used for the limited communicating purposes between two units. Automatic connection is made when one handset is picked up, and causing the second unit to ring. The received indication (Tone-ring & Lamp) is furnished on all models.