Canteen? Thermos? Decanter?

I picked up this item at auction, and I can't tell if it's an old canteen, liquor decanter, or something else. It's copper on the outside with brass decorative straps. It has a brass screw top. It stands 9" high and 4" in diameter. There are no makers marks.

It has some type of grey metal liner. Even though the outside is dented all over, the inside liner is still smooth, leading me to believe there's an air pocket between the liner and the copper exterior. If it were a canteen or thermos, that would provide some primitive insulation of the contents. However, seeing that the opening doesn't extend much past the top, it would not be easy to drink through. Any suggestions or guesses are appreciated.