Religious garb and U.S. military uniform regs

[Elendil's Heir]

Are Sikh men serving in the U.S. armed services permitted to wear their turbans while in uniform? Are Muslim women allowed to wear the hijab? Are Jewish men permitted to wear yarmulkes? Are they permitted to do so on some occasions (such as worship) but not others?

[silenus]

Goldman vs Weinberger (http://law.jrank.org/pages/12591/Goldman-v-Weinberger.html)