Under arms explained

Under arms describes a state of military readiness (actual or ceremonial). Typically, troops are considered "under arms" when they are in uniform, on duty, and carrying a weapon (rifle, side-arm, or sword), as opposed to being in uniform, on duty, but not carrying a weapon.

Soldiers not actually carrying a weapon but wearing a service belt or web gear associated with carrying weapons may be considered to be symbolically "under arms".^[1]

Soldiers normally remove headgear while indoors; however, soldiers who are under arms normally wear their headgear indoors,^[2] with a few exceptions.^[3]

Notes and References

1. Web site: Marine Corps Uniform Regulations . Byrd . Roy R. . 2003-03-31 . . 7–10 . 2013-08-02 . The leather service belt is the standard sword belt for officers and may be issued to SNCOs and NCOs for ceremonies, parades, honor guards, and reviews when the sword is prescribed, and upon other occasions when an individual is actually or symbolically 'under arms.'.
2. Web site: Uniform Regulations . Neptun . Daniel A. . February 2009 . . 2-1 . 2013-08-02 . [Headgear s]hould not be worn indoors or in no-cover areas unless under arms . https://web.archive.org/web/20130616005319/http://www.uscg.mil/history/docs/2009USCGUniformRegs.pdf . 2013-06-16 . dead .
3. Web site: Drill and Ceremonies . 2012-01-20 . . A-3 . 2013-08-02 . Officers and enlisted men under arms uncover only when ... Seated as a member of (or in attendance on) a court or board [or] Entering places of divine worship [or] In attendance at an official reception..