The MC3 Multi-Channel Crypto Controller was made by Dataproducts, New England. The MC3 was a 16 channel, time domain multiplexor being constructed to MIL-SPEC's and TEMPEST. Being  one of the first microprocessor controlled muxtiplexors, it was good unit in it's heyday. Asynchronous and synchronous data was supported by the device. Normally the MC-3 would be run on the red side of the circuit with the "trunk" being normally connected to a KG-84. It could also be used with non encrypted multiplexer inputs.

MC-3 control panel. (Photo via E-bay)

The complete MC3-assembly (Photo credit unknown)

Oct 27/10