Use the noun armament to talk about the kind of weapons that armies use when they wage wars. A tank, for example, is an armament.
The word armament is good for describing heavy duty weaponry and the equipment that's associated with it, like bombs, fighter jets, tanks, and assault rifles. It's even more common to use the plural form, armaments. In the seventeenth century, the word was mainly used to mean "naval force equipped for war," and it comes from the Latin root armare, "to arm, or to furnish with weapons."