[GreenKeys] RADIO TELETYPEWRITER AN/GRC-46

[NNN7DXB at aol.com]

All:

To expound a bit on what Duncan just mentioned:

For those who don't know, the AN/GRC-46 is a Radio Teletype set (rig)
that was originally mounted on the M-37 series 3/4 ton truck. The
AN/GRC-46 was used primarily by the US Army in tactical units. Power
was supplied by a 5 KW generator set on a trailer. This equipment was
in use until about 1969. After that, it was superseded by the AN/GRC-142
which was an upgraded model with the same capabilities. Primary
Teletype equipment was Kleinschmidt TT-98/FG printer and TT-76/C
Reperforator-Transmitter (TD), or any of their variants. Crypto gear
was the usual TSEC/KW-7 - for both the AN/GRC-46 and AN/GRC-142.
Operating speed was normally 60 wpm (45.5 Baud). Some European
export models were set up for 66 wpm. These rigs were common in 
the Army and could be found in Signal, Infantry, Artillery, Armor,
Quartermaster, Aviation and Test and Eval units. They were used
for message handling in most units, for spotting, targeting & TACFIRE
in Artillery units, and for Aviation Weather operations in Army Aviation
units. Most times, they were employed in Army Command/Operations
and Administrative/Logistics RATT nets. Often times, they were
co-located with tactical CommCenters in the field environment as one
of the (commcenters) various means sections. More than AN/GRC-46
or AN/GRC-142 were in proximity when working with commcenters.
When commcenters circuits went down, RATT picked up the slack;
When commcenters were swamped with traffic (especially Routine
traffic), that traffic was moved over to the RATTs which as overflow.
Most RATTS in tactical units were redundant to most tactical commcenters;
this means, where there was a tactical commcenter, there was also
a RATT at the same location, so traffic could always mover over either
RATT or the commcenter, commcenter being the primary system of
choice. Both the AN/GRC-46/142 were One-Way-Reversible (OWR)
operations only, or what we in the commcenter usually called "half duplex".
You could only send or receive at a time, but could not do both with the
same equipment. These systems worked on High Frequency (HF) only.
Later model AN/GRC-142s had provision for a wire-line "pony" circuit
to the commcenter, which was usually unsecure (since the RATT and
commcenter were inside the same SECURE perimeters when operating
together).

On the Y side (DSSCS), RATTs were used for Intel traffic to pass Exercise
COMINT traffic in the field; they also passed intercepted G-2 Weather
traffic and sometimes supported Corps and Division SWO operations.
In Europe, Russian Weather from RUMS was often intercepted by G-2s
at both Corps and Divisions levels. RUMS was the call letters for a large
and powerful HF Russian weather transmitting station in Vladivostok 
during the Cold War. It transmitted synoptic WX data at 60 wpm, clear text.
(The Russian RUMS not to be confused with the large US Army tape relay
at Phu Lam, with the Routing Indicator RUMS, 1959 thru 1970).

These rigs could also be used for passing tactical Intel (enemy sightings,
grid coordinates for patrols, and other tac-intel operations in the field;
as well as other Intel Operational and Informational traffic). The AN/GRC-
46s and 142s did not handle GUARDRAIL traffic, nor did it support any
of the TROJAN operations in the tactical units.

Hope this helps.

Dave