under arms

under arms (not comparable)

1. (military) Equipped with weapons (of a country, army etc.); in a state of armed, military readiness. [from 17th c.]
   • 1792, Charlotte Smith, Desmond, Broadview, published 2001, page 325:

     They were preceded by a small party of the national guard, in their uniform, and under arms.

   • 1998 September 20, New York Times:

     The Taliban have only about 40,000 men under arms.

2. (chiefly Australia) Carrying a weapon (chiefly of a criminal); of a crime, committed using a weapon or weapons. [from 19th c.]

• under arms on Wikipedia.Wikipedia

• Rudermans, snare drum