Ground Mobile Forces

'Ground Mobile Forces (GMF) refers to the tactical satellite communications (SATCOM) component of the Tri-Service Tactical (TRI-TAC) program. Developed by GTE-Sylvania in the mid-1970s, TRI-TAC was a joint-service military command, control, and communications initiative. 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.

Architecture and technical specifications

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

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.
Spoke Terminals (AN/TSC-93B and AN/TSC-94A): Designated remote terminals that connect directly back to a hub.

Data capacities and throughput

Hub Performance: Standard hub configurations ingest up to 48 multiplexed, encrypted channels from a maximum of four spoke terminals simultaneously. Utilizing an external multiplexer doubles this capacity to 96 channels.
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.
Spoke Performance: Outlying terminals support up to 24 multiplexed channels (16/32 kbit/s).

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)	20 ft (6.1 m) QRSAG dish
Spoke	AN/TSC-93B / AN/TSC-94A	Remote Spoke	24	8 ft (2.4 m) parabolic dish

Radio frequency and environmental protection

GMF terminals communicate via Super High Frequency (SHF) X-band through the Defense Satellite Communications System (DSCS) satellite constellation.

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. To support sustained tactical deployments, equipment shelters are sealed for operations in Chemical, Biological, Radiological, and Nuclear (CBRN) environments.

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.

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. Despite their technical obsolescence, select GMF terminals remained active in field operations under severe conditions during military engagements in Iraq and Afghanistan.

References

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Ground Mobile Forces, Wikipedia, The Free Encyclopedia.
↑ DSCS-3, GlobalSecurity.org.

"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.

[wp-gmf-1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Ground Mobile Forces, Wikipedia, The Free Encyclopedia.

[globalsecurity-2] DSCS-3, GlobalSecurity.org.