My brother bought me three NATO watch straps from Gnomon Watches for Christmas, and feeling like none of the watches in my "collection" (I use that term loosely) were up to par with how awesome the straps are, I picked up this watch last week from a local antique shop.
It's a silver Seiko Sportsman manual wind watch with the seahorse back case. From what I've been able to gather from the internet, it is most likely from the 1960s. It is in very good condition externally, and seems to be running well, though it does lose 4-5 minutes over 24 hours, but I can live with that for now. It's also a good size and looks cracking on a NATO strap (as can be seen in the picture). I like the resemblance that it bears to some of the older Omega Seamasters, like the one below (not mine).
I apologize for the picture quality as I am currently without my normal camera since my brother took it with him to London for the month of January, so I did the best I could with his camera (not that my normal photos are anything to write home about). If you actually have any more info on this watch, I would really love to know more.