I think this question boils down to this: Do your actions have a net positive or a net negative affect on the world? Does working at this company in some way offset the harm that the company is doing downstream? In this case I have a hard time coming up with a reasonable way in which this might be the case. Paying you and your family to have stuff doesn't offset causing actual death and physical harm.
I mean ... not saying I necessarily agree, but isn't the logical counter argument being defense and deterrence?
I use to be much much more ideologically against arms production, but honestly, seeing what's happening in Ukraine has given me some pause and caused me to reflect a lot. When a tyrant like Putin can amass a huge amount of weaponry and just decide to invade and impose a totalitarian dictatorship on a neighbouring country, and the only thing that has stopped him is a mass amount of better weaponry, it muddies the moral waters a bit.
This is true, but on a personal level I have no idea how to do the calculus for, "My work is killing people, but it would have been worse if it hadn't." I think the show "The Good Place" got it right and it is just too interconnected and complicated to actually derive an answer as to whether an action is net negative or positive. That said, if I had to place money on a given action being negative, working for an arms manufacturer would be one I'd be fairly comfortable betting on.