Sorry to have to tell you, that specific version of "anchor button" is definitely a civilian-usage Nautical-motif "Fashion" button, from sometime in the first half of the 20th Century. It's been posted many times during past years here in the What-Is-It? forum. A major clue to its actual identity: it always has/had an iron/steel back, which is most often either rusted away or only partially present. Note the small diamonds and other symbols encircling the anchor... definitely not a Military button.