Vintage US Military button fly zipper leg pants D100 Unknown Era Army ? Rare

Solid vintage condition. Seems that all pockets have either zipper or button closures. Pretty sure these were for special operations of some sort. I’ve never seen this specific style before. Waste is between 36-38” as there are no size tags. Inseam is approximately 30”. Questions welcomed and additional pictures if needed. These are quiet interesting & built heavy. I ship within a day of purchase. B6