1MC is the term for the shipboard public address circuits on Naval vessels. This provides a means of transmitting general information and orders to all internal ship spaces and topside areas, and is loud enough that all embarked personnel are able to (normally) hear it. It is used to put out general information to the ship’s crew on a regular basis each day. The system consists of an amplifier-oscillator group which is located in the IC/gyro room, a microphone control station, portable microphones at each control station and loudspeakers located throughout the ship. Control stations for the 1MC announcing system are located at the pilot house, OOD stations on the quarterdecks, after steering and Damage Control Central area. The term "MC" is an acronym for Main Circuit.
During an incident involving a casualty, the 1MC is a valuable damage control communication tool used by DCA (damage control assistant) to keep ship members alerted and informed of casualty location area, updated status, and incident response efforts by the DC organization.
The 1MC is divided into smaller sub circuits, such as officer's quarters, and topside. At the option of the officer of the deck, some words are not passed on certain circuits.
Even with the importance that the 1MC carries not every speaker works or can be heard.
However this being said it is still every sailor’s duty to know what is said over the 1MC. Of course the when it is time for that most popular of all 1MC calls, “Liberty call, Liberty call. Liberty Call for all hands, Liberty to commence at 1630.” Everyone will hear that.
Getting this into your every day talk might be hard if you do not have a system like this at work. But if you do you should be able to work this one in. “Hey Bob what did Sally just say on the 1MC?”

























