RATT RIG

Post WWII US Army Radios & Radio Teletype Shelters

 

M37 w/grc-46

The AN/GRC-46 Series

The AN/GRC-46 series is a Radio Teletype set (rig) that was originally mounted on the M-37 series 3/4 ton truck. It was later mounted on the M-715 and various CUCV's as a stopgap measure while the M-37 was phased out and the HUMVEE phased in.  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 or from vehicle power. This equipment was in use until about 1969 although reserve and NG units had it beyond 1969. After that, it was superseded by the AN/GRC-142 which was an upgraded model with similar capabilities.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 with earlier models having the TSEC/KWB-9.  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, National Guard and Reserve and could be found in Signal, Infantry, Artillery, Armor, Quartermaster, and Aviation 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 Comm Centers in the field environment as one of the (Comm centers) various means sections. More than one AN/GRC-46 was in proximity when working with Comm Centers. When Comm Center circuits went down, RATT picked up the slack. When Comm Centers were swamped with traffic (especially Routine traffic), that traffic was moved over to the RATTs as overflow. Most RATTS in tactical units were redundant to most tactical Comm Centers; this means, where there was a tactical Comm Center, there was also a RATT at the same location, so traffic could always mover over either RATT or the Comm Center, the Comm Center being the primary system of choice. The AN/GRC-46 is One-Way-Reversible (OWR) operations only, or what we in the Signal Corps 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. (courtesy Dave Freed)

The "Plain" Model

The first or "plain" model had the security equipment installed under the TTY rack.  In the models I saw in the 60's, there were three fold down seats or "jump seats", plus a storage box.  Shelter doors swing to the left on S-89 shelters and the to the right on the S-144 shelters.  The fuel tank for the heater is mounted on the inside of the door in the early models and outside of the shelter on later models. The S-89 shelters were steel.

46 Plain Layout

The 46 "Plain"

The "A" Model

Same as the "Plain Model" except in the "Lightweight" S-46A Shelter

The "B" Model

Early documents say the "B" is the same as the "Plain" model except mounted in the S-144 aluminum shelter.  Pictures and parts lists verify this, however, some were modified as the road side operator seat was removed in some "B" models and the crypto gear rack installed in it's place.  There was still a shelf under the RTTY gear for the J-1195 interface, mounted under the TT-76.  Also, the storage box was replaced with a two drawer file with one drawer having a combination lock.  The TT-98 was receive only in the modified sets as the keyboard was taken out of the loop. All transmission was from the TT-76. Some "Plain" models were upgraded to "B" with MWO's.

The J-1195 Crypto Interface and the J-1194 Remote Interface from the "B" Model - Rare

J-1195 Crypto Interface     J-1195 Crypto Side ViewJ-1194 Remote Interface

One Version of the 46B

Another Version of the 46B

The "C" Model

The curb side and rear jump seat was removed in the "C" model and the new style crypto gear rack installed in it's place. The shelf under the RTTY gear was removed.  Also, the storage box was replaced with a two drawer file with one drawer having a combination lock. The TT-98 was receive only as the keyboard was taken out of the loop.  All transmission was from the TT-76.  Many earlier models were upgraded to the "C" with MWO's.

AN/GRC-46C

The 46C