A field like yours requires mostly higher education to progress. A lot of degree holders in materials science end up in semicon production type jobs, which is almost sunset industry. You have consider if you really want to make a career where a dip might just not be enough. Given you have started so late, you need to be careful with your choices and not much time for experimentation.

Since you have serve ns and kind of comfortable being in the army, it would be a much better and easier career choice although I usually advise against people being regulars. That would have more stability and progression among all the options you have suggested.