Help to ID/Appraise a flask

[ClintonHammond]

I've had this for a while... Got it off an old chum when his dad died... said it had belonged to his grandfather.. possibly from "The War"???

Pic Here

The only 'mark' on it is the number 4 in a circle on the bottom...

Any ideas? Any hints? Anyone care for a mint?

 

[ClintonHammond]

Nothin' at all?

wow...