That makes no sense since the vote is secret. Register as an Independent.
I never agreed with this view, but from thier perspective, choosing a candidate and casting a vote impinge upon the apolitical nature of the military. It is an ironic view, given the effort DOD puts into voting assistance effort. However to a minority of officers and career NCOs it is an article of faith.
Personally, I always voted, but kept my political opinions to myself and my wife. I did have to occasionally chew the asses of junior officers and NCOs who ran off at the mouth about political issues in front of their subordinates, or brought thier opinions into the workplace (even if I thought they were right). Partisan politics has no place within a military organization.