Not sure if commercial or some kind of P51 Air Force cover(which I've never heard of). Has snap closures which is wrong for P51, no way to hook to a belt, but has the strap buckles on the sides as seen on P51. Never seen anything like it before. Looks like the same blue/gray canvas from my other AF webbing...also lined with nice gray felt. Well made, but I'm leaning toward commercial.
I stuck a modern US canteen in it to make it easier to shoot.
I stuck a modern US canteen in it to make it easier to shoot.