This one "has it all". The button dates, probably to the early 1850's and maybe before that. It has a Scovill (rmdc) backmark, dating it to well before the Civil War. 100% gilt remains, the shank is perfectly straight, the backmark is entirely legible and there is even some original string attached. I do not believe this string is thread from a uniform. Rather, I would opine that the officer or seaman who owned this button kept a few extras on a string for replacement purposes. This one is likely not to have seen service for it looks as nice as the day it was manufactured.

If you like your buttons in dead-mint condition, here you go. I have several more "navies" coming, but no others with rmdc backmarks like this.

A collection of naval buttons from the earliest days of the United States to the post Civil War era would make a fascinating and very educational display. And if someone has such a collection, I have not seen one displayed at a Civil War show. Perhaps you're the one to start building it!