This is the 2917th most frequent Russian word.
вооружении
"Вооружении" means "armament" or "weaponry."
Here, 'на вооружении' refers to 'being equipped with,' indicating that the army possesses and uses modern missiles in its arsenal.
У армии этой страны на вооружении находятся современные ракеты.
The army of this country is armed with modern missiles.
In this sentence, 'на вооружении' is metaphorically used to mean 'equipped with,' referring to having strong arguments at one's disposal.
Для успешного ведения переговоров нам нужно быть хорошо подготовленными и иметь на вооружении сильные аргументы.
For successful negotiations, we need to be well-prepared and armed with strong arguments.
The word 'вооружения' refers to 'armaments' or military weapons in general, indicating the subject matter of the designer's developments.