It's Aussie mate, its called an echelon bag.
I am actually chasing one of these if you are up for a trade let me know
thanks for the info luke I'll keep a trade in mind mate and will let ya know .
These have only recently been superseded by the longer Dive bag.
Although the metal zipper is typical of 1970's Ech' bags, later examples have the plastic zipper.
'Echelon' as the zone of battle is divided up into A, B, C Echelon etc depending on how far back you are from the actual fighting-the bag would be left at B or C so the soldier could access it for resupply/changes of clothing etc.
Thank you Lithgow, I always wondered how it got that name.