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maritime DC & PPE Information Center


Intercommunication System (MC Circuits)


Many older designed ships have the Intercommunication System which is a two-way, station to station circuit operated by the ship's AC and DC electrical system. The intercom units (MC Circuit), also known as squawk boxes, are subdivided into the circuit designations below. The damage control organization utilizes the 4MC circuit to provide fast, dependable, command and control two-way transmission between DCC and each Damage Control Repair Station (DCRS). Additionally some ships have the capability to communicate between the DCRS and their satellite Damage Control Unit Locker (DCUL).

Intercommunication System Circuits:

  • 4MC - Damage Control

  • 19MC - Aviation Ready Rooms

  • 20MC - CIC

  • 21MC - Captain’s Command

  • 22MC - Radio Central

  • 24MC - Flag Officer

  • 26MC - Machinery Control

  • 29MC - Sonar Control and Information System

  • 30MC - Special Weapons Control Announcing System

Image of Intercommunication System

For more information, see the Index.