Although your find sorta resembles a US Navy uniform button, in actuality it is what button-collectors call a Civilian-usage Imitation Navy button, one of the varieties of "Fashion" button. For whatever it's worth to hear, your find is very common... it has turned up dozens of times in T-Net's "What Is It?" forum over the years I've been posting there.
If there is one button found by more hunters this is it. I think there was a major explosion at the plant and these buttons were scattered over the whole United States? It was my first "Navy" button until the knowledgeable people here informed me of its actual use. They busted my bubble but it taught it to research and learn what I can about relics, buttons in particular. I just wish I could remember half of what I learn!