squeaker - sorry your recipe has turned in a discussion of military history!
In the US military SOS was originally
creamed chipped beef. It's first use in the military appears to have been in the 1910 edition of the "Manual for Army Cooks". It was a little more elegant than what it would later become - beef stock, condensed milk, roux, pepper, parsley, and the chipped beef added at the last minute so the salty taste didn't overpower the dish.
By the 1940's it was a little less elegant. In the field it had been reduced to just roux, powdered milk, black pepper and chipped beef - and some of the cooks were soaking the meat overnight to reduce the saltiness although it was not a part of the recipe in the manual.
It appears that beginning in the late 1960's some parts of the US military began to use hamburger (the recipe was: creamed ground beef) as well for the dish that people called SOS. So, for those who thought I was doubting you - here is your vindication and my acknowledgment.
Dove - I grew up waiting for the Eagle to Fly! I know what you mean.