I work at one of the many aerospace companies that do work in the commercial, government research, and defense sector. I've been with the company for a little over a year and in that time I've been fortunate to become a vital member of at least one project.
As of recently, I'm able to work on certain classified projects that my management has hoped I would be able to join eventually. These projects vary in subject and I know very little about them, but I do know the one that I'm slated to join soon I'm joining simply because of timing and the need they have on that team. The issue is, the project heavily involves a variety of weapon systems and it's not the type of project that I ethically support or feel personally comfortable working on.
I used to work for a different company in the same industry for two years that was more defense oriented than my current company and one of my primary reasons for leaving was my personal unhappiness with being involved in the work the company was doing. I didn't tell that to my new employer as I was afraid it would come off as unprofessional and since this employer has a good variety of non-defense work, I thought I could just avoid the work I'm uncomfortable with.
Now I'm trying to figure out how to bring this up to my manager. Because I know that if this project becomes a long term project I'm involved with, then I'll be unhappy and probably looking to leave eventually. I'm fortunate that my manager is a thoughtful one and has told me multiple times in the past that I essentially don't ever have to be stuck on projects I don't want to be stuck on or take on work I don't want. Obviously in practice you take on the ugly work too, but it's nice to know the option to turn down work is there.
I'm just not sure if it comes off as unprofessional or hostile to tell my manager that I don't personally feel comfortable working on a project so involved with weapon systems. I'm afraid it may come across as hostile because a number of my managers and mentors at work take on similar work without issue (as far as I can tell). I'm still willing to work cleared programs, it's just my criteria is a personal one and having my manager try to figure out if a project matches my personal ethics before assigning me anything feels like it could be an unprofessional and uncomfortable situation.
Additional notes/nuance:
I'm willing to offer to work on this project short term, as the need is there, if I can transition off of it within an agreed to timeframe
I feel valued at work and I think that management would much rather have me there continuing the same work I currently do than have me leave
I value sticking to my principles on this much more than I value avoiding the potential career harm this may cause
I currently work from home. Any cleared work will require me to come into the office. If possible, I'd like to make it clear to my manager that I'm fine coming into work (many of my older coworkers do and I'm at much lower risk than they are), it's just this particular project/topic that I'm uncomfortable with.