Hi WBT - It could have been the RS-6 set you were using. Back then, MARS operators you worked would have been CW qualified. The GRC-109/RS-1 referenced at the beginning of this thread was in service for a long time and it is a contemporary of the smaller RS-6. Incidentally, two equipment cache containers were recently sold on EBay. They had been found in the attic a building in Austria and had been cached there in 1961. The cache included a complete RS-6 set as well as a comm plan, crypto encode/decode materials, one-time pads etc.
A pretty interesting "find".... There is a CIA FOIA declassified release with the contents - including radio serial numbers - of this particular cache.
I have some info in a post on the RS-6 here - it includes a photo of the Austrian equipment cache.
http://www.n6cc.com/the-rs-6-radio-set
Does that set look familiar?
Thanks for your service..!
Tim