TAC 1, shown in Reply 2, is the primary tactical channel. TAC 2 is the secondary tactical channel, used to avoid interference at a second/nearby incident and occasionally as a second tactical channel at a major incident, but the latter usage is rare.
The Department often retransmits major incident tactical channel traffic (normally TAC 1) on one of the six talk groups comprising the Department Administrative Radio System (DARS) in the 400 mHz trunked radio system. Either talk group 4880 or 4896 is usually utilized.