Well there you go Eric, I looked everywhere for a manufacturers mark or an NSN (NATO Stock Number) and had to go back to take a closer look. They were used in Vietnam, and my first one was much older, but after a vehicle accident on an exercise, some "Light fingered Larry" removed my old knife, so I had to get issued another one, and I've just checked with my magnifying glass, it says "Ontario 5-94" which sounds right, as I was issued that one in '95.
Here are a few more I've found in various drawers.
More knives by
Terry Prendergast, on Flickr
I love the top one, it looks like something that Winchester would have designed, I think I picked it up at a swap meet for 2 bucks. The one beneath it was a "Wish" cheapie, or it may even have been a freebie, the third one was a gift from the guys doing the implementation of the new PC-21 aircraft training system, and I like that they didn't cheap out, they had Victorinox, the makers of the original Swiss Army Knife, make them.
The last one is a little folding box cutter which I was always using when I was managing warehouses. If I left a standard box cutter down for more than 5 minutes it would disappear, so it was handy to have one in my pocket at all times.