My Dad, who was in the army just prior to WWII, spoke often about the SOS he enjoyed while in the service. In fact, he liked it so much that he made it at home quite often…we all loved it. He used ground beef. My guess is that he did that because (a) it was far less expensive than the dried stuff, and (b) it was what he had in the Army. He was in the Army engineers and spent a lot of time in Washington State out in the "field." They would get their food locally. Perhaps ground beef was more easily found in the rurals than the dried stuff.