Echelon above corps.
TRITAC operates at echelons above corps (EAC). (page 1-31, para 1)
Theater communications system (Army).
communications system (Army)(TCS(A)). (page 1-52, para 1a)
The TCS(A) consists of an area network and designated command links.
(page 1-52, para 1a)
AN/TTC-39 circuit switch is the heart of the multichannel switched
network. It provides a means of connecting telephones, message traffic,
and data users in both the secure and nonsecure modes in the AC area
network. (page 141, para 2a(l))
Theater signal command (Army)(TSC(A)).
The theater Signal command (Army)(TSC(A)) is responsible for providing
communications support to the theater army at EAC. (page 1-54, para 1d