This is a Soldier, made by Elsener (which was renamed Victorinox AG later on). The 1891 model of the soldier’s knife was 100mm in length and had wooden handles. The redesigned model 1951 was slightly smaller (93mm) and had brown fiber scales.
The one in the picture has fiber scales but measures 100mm. Also, there is no year stamped on the main blade, which all knives made after 1920 usually had. So, I don’t really know when this one was made.
It’s a bit dirty but actually it’s in pretty good shape considering its age. I think the small imperfections (on the blade for example) add a bit of character to the knife. Also, it’s not stainless steel but carbon steel as you can see in the pics.
This SAK is SPF.