TRI-TAC (Tri-Service Tactical Communications) is an obsolescent military tactical communications architecture, centered around AN/TTC-39 digital circuit switches. The AN/TTC-39 is a modular design, which, in a late version, handled in excess of 700 lines — comparable to a private branch exchange of moderate size. TRI-TAC would interconnect tactical command posts to one another, to higher command, and to the communications centers linked by radio to moving forces. It can switch low-speed data (i.e., 16 or 32 Kbps) as well as digital voice channels, and a limited number (i.e., 96 of 744) analog voice circuits.
The switches differ from those in commercial use, in that they are:
- Transportable (i.e., cannot operate "on-the-move", but can be moved from site to site)
- Have integral encryption
- Operate with satellite and terrestrial radio as well as multiplexed digital signals on copper cable
It interoperates with the smaller Mobile Subscriber Equipment switches, and is being replaced, incrementally, by the AN/TTC-56 switch and Joint Network Node, on the way to the fully packet-switched Warfighter Information Network–Tactical.