An interesting looking watch:
The case is bare base metal (zinc in colour) - can't find any signs of it's previous colour / plating
The watch strap bars are "fixed" so you'll need an appropriate strap (e.g. open ended; NATO...etc.)
It's military in style but there is no pheon so not military issue
The case back is actually screw not flip (I can see some scratches on the back - possibly from a knife)
Working fine - ticking along quite nicely but probably well overdue a service (very good time keeping over 12 hours though)
The crown stem doesn't seem to be locating properly but it is still possible to wind it up - the crown requires attention or replacing (this could well be a replacement)
Case dimensions approximate: