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It looks a legit Navy jacket to me, but it could be a later issue and not a WWII jacket.
It has the "USN" stencil (without dots, instead of U.S.N.), the zipper looks a later heavy duty type, and the tag has a N140 contract number with two sets of numbers instead of the usual NXSX navy contract code.
Here there's a discussion - with no definite conclusions - about navy contracts and N140 codes: http://www.usmilitariaforum.com/forums/index.php?showtopic=1590&st=0
So I suppose it could be a '50 jacket.