I think it's probably a specialist pouch of some sort. I know there are all sorts of different issue pouches for communications equipment, night fighting gear, engineer tools etc., hell, there's probably an issue belt mounted knife set for the combat caterer. Without an NSN to refer to it will be hard to find out. The marked number on the rear may even be the serial number of the piece of equipment it was meant to carry.
Kammo-man is right - how do you type under all that stuff!?