Weaponry means weapons taken together, as a class of equipment — the guns, missiles, bombs, tanks and so on that an army, a country or a group has. It is uncountable: you say 'modern weaponry', 'advanced weaponry', 'the weaponry of the Roman army', never 'a weaponry' or 'three weaponries'. The word belongs to serious writing — news reports, history books, military and political discussion — and it feels heavier and more technical than the plain plural 'weapons'. The difference is small but real: 'they had weapons' points at the objects; 'their weaponry was outdated' points at the whole set as a kind of equipment, and invites you to judge its quality or level. That is why it sits so naturally after adjectives like sophisticated, heavy, nuclear, conventional, primitive. People also use it playfully outside war — a chef's weaponry of knives, a comedian's weaponry of jokes — but that is a stretch for effect, and the reader should feel the joke.