I bought this original Soviet Officer Leather Bag from our local Estonian twice a year held old cars and antique fair. In Russian it’s called “Planshet” – map-case and it was used for carryng different documents, pens and other essentials needed in the army. Seller told me the hole story of different bags used during the WWII.
For example this particular bag has a handle and long shoulder strap and it was used in infantry. But if this kind of bag has only one short handle it was used in air forces attached to a belt.