All About Pocket Knives

I have a case bone handled hunting knife with an interchangeable blade. My father (85) found it when he was a teenager and carried it with him in WWII. He even stamped his 4 digit service number on the blade.
What I`m wondering is when it was made and is it worth anything in its condition, which is worn but not cracked. I think they used to make a hatchet blade for it. It is egraved with a patent date of oct. 22, 1935
I am attaching a photo.
Sharpshooter

Hey Sharpshooter, I would think that was made sometime in the 30's to around 1940. Its a second cut stag knife-axe combo. If ya had the axe & sheath they all store in, and it was cleaned up, I have saw the complete set go for $700.00 I would bet if ya cleaned the knife only you have, just a guess, 150.00-250.00. Go to ebay in knives, swords, blades, type in Case knife-axe in the search. There is a few up right now. Stagman