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 abbreviation 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.
The 1MC is also used for transmitting various alarm sounds to alert the crew of specific impending dangers such as:
- Inbound anti-ship missile (VAMPIRE, VAMPIRE, VAMPIRE!!)
- Chemical attack
- Flight deck crash
Other MC Circuits
- 2MC - Propulsion plant
- 3MC - Aviators
- 4MC - Damage control
- 5MC - Flight deck
- 6MC - Intership
- 7MC - Submarine control
- 8MC - Troop administration and control
- 9MC - Underwater troop communication
- 18MC - Bridge
- 19MC - Aviation control
- 21MC - Captain's command
- 22MC - Electronic control
- 23MC - Electrical control
- 24MC - Flag command
- 26MC - Machinery control
- 27MC - Sonar and radar control
- 29MC - Sonar control and information
- 30MC - Special weapons
- 31MC - Escape trunk
- 32MC - Weapons control
- 35MC - Launcher captains
- 39MC - Cargo handling
- 40MC - Flag administrative
- 42MC - CIC coordinating
- 44MC - Instrumentation space
- 45MC - Research operations
- 46MC - Aviation ordnance and missile handling
- 47MC - Torpedo control
- 50MC - Integrated operational intelligence center
- 51MC - Aircraft maintenance and handling control
- 53MC - Ship administrative
- 54MC - Repair officer's control
- 55MC - Sonar service
- 58MC - Hangar-deck damage control
- 59MC - SAMID alert
- General Quarters - "This is not drill, this is not drill, General Quarters, General Quarters! All hands man your battle stations. Go up and forward on your starboard side, down and aft on your port side. General Quarters, General Quarters!" Generally The reason for General Quarters is given (such as Fire in Main Space 2).
- Sweepers - "Sweepers, Sweepers, man your brooms. Give the ship a clean sweep down both fore and aft! Sweep down all lower decks, ladder wells and passageways! Dump all garbage clear of the fantail! Now sweepers." Although most ships discourage throwing of trash over the side but instead use mulch/pulp rooms. In port "Dump all garbage clear of the fantail" is replaced with "Dump all garbage in dumpsters provided for on the pier."
- 8 O'Clock Reports - "Now lay before the mast (if the Captain is on board) all eight O'Clock reports. Eight O'clock reports will be received in the wardroom (generally)by the Commanding Officer."
- Personnel Working Aloft - "There are personnel working aloft on board (ship) , do not rotate, radiate, or energize any electric or electronic equipment, start gas turbines, or operate ship's whistle while personnel are working aloft on board (ship)." (Passed every fifteen minutes and by all adjacent ships)
- Divers Over the Side - "There are divers over the side, do not rotate screws, cycle rudders, take suction from or discharge to the sea or operate any underwater equipment without first contacting the Chief Engineer and the diving supervisor." (Passed every fifteen minutes)
- Reveille - "Reveille! Reveille! Reveille! All hands heave out and trice up. Reveille!"
- Taps - "Taps! Taps! Lights out! All hands return to their racks and maintain silence about the decks. Taps."
- Darken Ship - "Darken Ship! Make Darken Ship reports to CCS."
- Fire - "Fire, Fire, Fire, Class (A, B, C, or D) Fire in Compartment (Compartment Number and Nomenclature if known). Away the (at sea fire party, (Generally called "Flying Squad"), IET (Inport Emergency Team), or ships fire fighting team))provide from repair 2 (Or closest Repair Station not inside the Fire Boundary)
- Breakaway music - Popular music played at the conclusion of an underway replenishment evolution. It is used to motivate the crew.
- Submarine diving - "Dive, dive." (followed by two klaxon blasts then) "Dive, dive."
- Security Alert - "Security Alert! Security Alert! Away the Security Alert team! Away the Back-up Alert force! All hands not involved in Security Alert stand fast! Reason for Security Alert: (state reason)"
- Flight Quarters - "Flight Quarters! Flight Quarters! Set condition 1-alpha for flight operations! Set condition 1-alpha for hoisting and lowering of boats, port boat davit! The smoking lamp is out after frame 1-2-niner; all personnel not involved in flight operations stay forward of frame 1-2-niner! All personnel remove soft hats and refrain from throwing FOD material over the side!
- The following is a test of the helo crash alarm from the flight deck - disregard this alarm (test alarm sounds). Test complete - regard all further alarms!"
- The 1995 film Crimson Tide demonstrates in some detail the usage of the 1MC with regard to command instructions and ship wide orders.