[blantonl]

All TACSAT coms are done via single-channel Iridium networks at UHF.

Huh? Military UHF TACSAT communications are single channel UHF networks via geostationary satellites. But the military also makes extensive use of Iridium and INMARSAT networks to fill in gaps of bandwidth/availability coverage.

SATCOM / INMARSAT is heavily based on Iridium

Huh? No. Iridium is cross-linked Low-Earth Orbit (LEO) architecture. UHF Military TACSAT is geostationary dedicated transponders for the military - and those satellites also carry EHF/SHF payloads as well. INMARSAT is also Geostationary in the L and C band areas.