The problem with the C-7 was the restrictive size of its cargo bay. It could load a jeep and trailer, provided the windshield of the jeep was folded down (or so I heard). There was no available radio communications hut available that would fit in such an arrangement. The M-37 3/4-ton truck with a mounted AN/GRC-46 radio hut was much too large to fit. Plus, the equipment normally mounted in the '46 was not the equipment desired by most SF operations teams. They preferred the larger equipment normally mounted in the AN/GRC-26 hut that fit the deuce-and-a-half truck.
The Signal Maintenance Shop at Nha Trang was called upon to design and build a suitable radio rig for the STOL aircraft transport. I was assigned to build the prototype.
I began by listing the minimum equipment needed in such an application. Then I acquired an empty AN/GRC-46 hut that had been in storage behind our Comm Center. With the help of a few friends, we also 'acquired' a 4-wheel warehouse trailer from LSC (Logistics Support Center). The process was rather simple: We went over to pick up our day's supplies, loaded them on a trailer, hitched it to our jeep, and drove away. (The secret lies in looking like you know what you are doing.) The trailer was then disassembled and the axle assemblies mounted directly to the bottom of the hut. It was now exactly the right size to fit into a C-7 aircraft.
Then, I gathered the equipment to outfit the hut. The only item that needed modification was the T-368 AM/CW/FSK Transmitter. Since it was only going to be used for FSK, it was decided to cut it down and remove the AM modulator section. This would allow it to fit, as well as making it many pounds lighter. I stripped everything from the cabinet and hacksawed the excess section from the frame. I took the panels to the airbase machine shop for them to cut to fit. The frame was welded back together and the new panels attached. After a quick coat of paint, it looked almost as if it had been built that way. The main wiring harness was rebuilt to eliminate the extra wires. The one transformer that needed to be retained from the modulator section was mounted on a small metal panel to sit on the floor of the hut.
When reassembled, the transmitter worked better than new. With the elimination of the extra parts, the remaining components worked more efficiently. Wheras the original was rated at 500 watts, it usually ran around 450 watts output. With the modifications, it now put out around 510 watts (CW).
The transmitter, FSK modulator, demodulator, R-390 receiver, one teletype machine, and a complete Collins SSB KWM-2A set were installed in the hut. After a complete 'shakedown' in the Signal Company area, it was ready for field service.