[RSwank]

It is a parachute quick release buckle.

https://heritageflightgeardisplays.w...hute-acquired/


Same design was used by airborne units:
http://www.101airborneww2.com/equipment.html

and even the Luftwaffe, see last item on this page:
http://www.oldnautibits.com/stockarc...ogue=A&page=24