What’s that watch?

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Plucked this pic from FB. Saved it to blow up and try to deduce the watch being worn. What you think?

“SP4 Hendrick Greenwood eats his first hot meal in five days, Vietnam, September 8, 1967”
 
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Can't see much, but blowing up the photo, the BoR bracelet has folded outer links, so it's probably not Omega.
 
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Seiko?
Very plausible given the context, but I can't identify it based on the photo.