C3 command unit
Intended for reconnaissance 'Mechs or vehicles, the C3 command unit, also known as a C3 master computer, is the central hub of a C3 network and allows linked units to share radar and targeting data on the lance or company levels.
Normally carried by the lance commander, the C3 command unit is the hub to which three C3 slave units on other friendly 'Mechs can connect. However C3 command units can also be linked in this manner to expand the network, the command units of each of lance commanders can be connected to a second separate command unit carried by the company command 'Mech/vehicle. Due to complexity required to coordinate C3 networks, they cannot be expanded beyond company size, or multiple companies linked together, even with the addition of extra command vehicles. The limitations in unit size are part of the reason for the ComStar-developed Improved C3 Computer.
As well as serving to share the linked lance/companies targeting data, the C3 command unit also duplicates the function of Target Acquisition Gear and can designate a target for Arrow IV homing missiles and Semi-Guided LRMs.
A C3 command unit is typically carried by a heavy or assault 'Mech due to their larger size and weight, and its importance as the hub of a C3 network. Outright destruction or interruption by ECM of a command unit is quickest way to bring down the portion of the C3 network it controls.
C3 Emergency Master
The Dragon's foes were targeting 'Mechs that mounted the C3 master computer, rendering the entire network useless. To counteract this, the Dragon created the experimental C3 emergency master computer in 3071. By stripping out the TAG functionality and exchanging longevity for capability, the engineers on the C3EM team created a device that could step in as a temporary backup system for a C3 network. Though it occupies twice as much space and weighs twice as much as a standard C3 slave unit, the C3EM can (briefly) keep a traditional C3 network running in the absence of a C3 master computer.
The biggest drawback to the system is the tremendous wear and tear placed on the unit during its short life. After 60 seconds of use, the system processor is overloaded with data and shuts down. Another drawback to the C3EM is the fact that once it enters "master" mode, it cannot be deactivated. The C3EM will function as usual in a friendly ECM bubble, but a hostile ECM bubble will cause it to go into standby mode.
The C3 emergency master system costs 2,800,000 C-Bills.
C3 Boosted Master
Introduced by the Federated Suns in 3073, the C3 boosted master system was originally an experimental system that ignores all electronic warfare equipment, ECM suites, etc. Only the Angel ECM suite can interfere with its signals. C3 boosted systems can be connected into the same network as standard C3 systems, however, interference from any hostile ECM equipment will sever standard components from the network.
The additional hardware links and encryption equipment that allows the C3 boosted master to operate increased both the weight and bulk of the unit. The C3BM weighs 6 tons and occupies 6 critical hit slots. It also costs 3,000,000 C-Bills.
The C3 command unit is the core of a C3 network. Should it be destroyed, or knocked out as a result of a critical hit, the entire network of any vehicles pointing to the C3 master will also go down, unless other units happen to carry C3 emergency masters.
When any unit in a C3 network (the 'spotting unit') has an enemy within line of sight, all units within the same C3 network may target the spotted enemy using the range between the spotting unit and the enemy (rather than their own range to the enemy). In effect, for purposes of weapon range, all units connected to the network may fire at the target as if they were in the position of the unit in the network closest to the target.
There are exceptions. Minimum range and maximum range are both calculated from the firing unit to the target, not from the spotting unit to the target. Weapons cannot be fired beyond their own maximum range through the use of a C3 network. 
As mentioned above, the C3 master computer can also duplicate TAG functionality for use with homing weapons. No other C3 system has this functionality.
A C3 master computer is capable of working on a company level, if the master controls another master. Any C3 master controlling another master can ONLY be connected to masters; it cannot connect to a C3 slave unit while controlling another master unit. Master units being controlled by another master can connect up to three slave units, however (one connection points back to the master, the remaining three are for slaves).
A C3 master being controlled by a master can't control another master.
All of these bonuses are negated if the connection between the master and slave unit is disrupted by an ECM field, except for the TAG functionality of the master. This can mean a unit is within the ECM field, or the line of sight between slaved units, and the master passes through an ECM bubble.
- This article refers to a common object and addresses the object as a common noun. The preferred terms are "C3 command unit" or "C3 master computer" (except on section titles & table headings, where "C3 Command Unit" is favored).
- TechManual, p. 209, "C3 Computer"
- Tactical Operations, p. 298
- Tactical Operations, p. 405
- BattleTech Forums: "(Answered) Boosted C3 with Normal C3"
- Total Warfare p. 131-133 "C3"