When the country is in peril, the troops must move.
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Classical/literary. You'll meet it in historical fiction and chronicles, almost never in spoken modern Chinese. Modern equivalents: 武器铠甲 (weapons and armor) or 军队 (troops).
memory
戎 = warfare/weapons (the radical 戈 is a halberd); 甲 = armor/shell. Together: the gear of war.
