Are you against the U.S. military in particular or all militaries? This part makes me think the latter.
I don't think it's all that controversial or ethically dubious to believe, in general, that militaries need to exist and that they therefore need to train their members on how to operate weapons.
More specific arguments against particular militaries and particular weapon systems are more interesting.
At any rate, some of the "things" that militaries achieve are good, necessary and, arguably, properly achieved by violence and the threat thereof. Such as protection from external threats of tyranny (surely we can all think of one contemporaneous tyrant with a military?).
That means, I think, involvement in conventional weapons systems for some military can be fine. In the case of the U.S. military, I could see objecting in particular, but I wouldn't predict any real impact to U.S. foreign policy due to that sort of personal choice. The main benefit would be on a personal and, depending on the circles you travel in, social level.