Ground Mobile Forces

'Ground Mobile Forces (GMF) refers to the tactical satellite communications (SATCOM) component of the Tri-Service Tactical (TRI-TAC) program. ^[1] Developed by GTE-Sylvania in the mid-1970s, TRI-TAC was a joint-service military command, control, and communications initiative. ^[1] The program aimed to field advanced multichannel switched equipment, eliminate redundant acquisitions across military branches, and establish seamless interoperability between tactical and strategic communications systems. ^[1]

Architecture and technical specifications

GMF systems operate in a hub-and-spoke network topology. ^[1] In this configuration, a central hub terminal can simultaneously ingest up to four primary data feeds from outlying spoke terminals. ^[1]

Terminal classifications

The system utilizes four primary designated SATCOM terminals categorized by their operational role:

• Hub Terminals (AN/TSC-85B and AN/TSC-100A): Equipped for point-to-point and hub operations. ^[1]
• Spoke Terminals (AN/TSC-93B and AN/TSC-94A): Designated remote terminals that connect directly back to a hub. ^[1]

Data capacities and throughput

• Hub Performance: Standard hub configurations ingest up to 48 multiplexed, encrypted channels from a maximum of four spoke terminals simultaneously. ^[1] Utilizing an external multiplexer doubles this capacity to 96 channels. ^[1]
• Channel Configuration: Channels operate at 16 kbit/s or 32 kbit/s, translating to an effective true capacity of 48 kbit/s when accounting for protocol overhead. ^[1]
• Spoke Performance: Outlying terminals support up to 24 multiplexed channels (16/32 kbit/s). ^[1]

Terminal Type	Designation	Primary Role	Max Capacity (Channels)	Antenna Type
Hub	AN/TSC-85B / AN/TSC-100A	Point-to-Point / Hub	48 (96 with external mux) [1]	20 ft (6.1 m) QRSAG dish [1]
Spoke	AN/TSC-93B / AN/TSC-94A	Remote Spoke	24 [1]	8 ft (2.4 m) parabolic dish [1]

Radio frequency and environmental protection

GMF terminals communicate via Super High Frequency (SHF) X-band through the Defense Satellite Communications System (DSCS) satellite constellation. ^{[1] [2]}

All GMF terminals feature external interfaces for field telephones, a 70 MHz Intermediate Frequency (IF) wideband input, and connection to an AN/TSQ-111 Tech Control Facility. ^[1] To support sustained tactical deployments, equipment shelters are sealed for operations in Chemical, Biological, Radiological, and Nuclear (CBRN) environments. ^[1]

Obsolescence and legacy

While legacy TRI-TAC and GMF hardware provided foundational field communications for decades, the bulky circuit-switched equipment has largely become obsolete. ^[1]

Over time, these systems were largely phased out in favor of modern, IP-based fly-away quad-band systems equipped with compact routers, switches, and advanced encryption hardware. ^[1] Despite their technical obsolescence, select GMF terminals remained active in field operations under severe conditions during military engagements in Iraq and Afghanistan. ^[1]

See also

• Defense Satellite Communications System
• AN/TTC-39 Circuit Switch
• Tactical Communications Network

References

1. Ground Mobile Forces, Wikipedia, The Free Encyclopedia.
2. DSCS-3, GlobalSecurity.org.

Further reading

• "AN/TTC-39 Technical Manual / Document" (PDF). Archived (PDF) from the original on February 11, 2026. Retrieved July 29, 2026– via RadioNerds.
• Carestio, R.; McLeskey, F.; Coyle, D. (16 June 1986). An Analysis of Planned Army Ground Mobile Forces (GMF) Satellite Use in Support in Mobile Subscriber Equipment (PDF) (Report). M/A-COM Government Systems, Inc. Archived (PDF) from the original on 26 August 2022. Retrieved 26 August 2022– via Defense Technical Information Center.
• Shively, Robert G. (15 April 1993). Updating The Joint Common User Communications Architecture — A Case For The Army's View (PDF). United States Army War College (Report). Carlisle Barracks, Pennsylvania. ADA263904. Archived from the original (PDF) on 1 March 2021. Retrieved 24 August 2022– via Defense Technical Information Center.