Although your button's front has a Navy motif (a "fouled" anchor), it has what button collectors call an iron self-shank back... meaning, the back itself form's the shank/loop for sewing the button onto clothing. (Holes are pierced in opposite sides of the dome, allowing thread to pass through to attach the button onto cloth.) No actual Navy buttons have a self-shank back. Note the raised dome in the center of your button's back, and compare it with the photo below. That form of self-shank back was invented and patented in the early-1900s, and is still in use today.