Your button has what button-collectors call a "self-shank" back. It means the instead of having a wire loop for attaching the button to clothing, the button's back itself is pierced with holes for sewing the button onto cloth.
It is believed that no actual US Military buttons were issued with a self-shank back. (That type doesn't work well for fitting through buttonholes on thick Military Uniform cloth.) The belief seems to be supported by your button's front showing weak detail, even though it is not a corroded button. Actual US Military buttons were manufactured to meet high quality standards, which includes having a sharp crisply-detailed stamping of the emblem (not an el-cheapo weakly detailed emblem). The high quality-standards for actual US Military buttons also specify "heavy-duty" construction... and self-shank backs are not heavy-duty.
