Unusual Medical Corp or Medic instrument, What is This Thing ? Bin 2

Description

Will only send to a US address.
I have no idea what this item is, but believe it is some kind of Medical Corps item as it came with a lot of Medic Gear, US Army
In the closed position it measures about 7 x 10 inches. There are two metal buckles that hold the item together. There are two internal springs, within the canvas and in order to open the item you have to overcome a substantial amount of spring pressure. When unlocked, the two sides open up like book ends, and a piece of canvas, that looks like you could slide a hand in is revealed. There is only one strap and it is attached on both ends to the "book cover type" ends. So the only thing that strap can do, it seems to me---is to bring both ends closer together as it is cinched down. Have never seen one of these things, and can't figure it out. Can't see any markings.