Serving in the military and being a conscientious objector

Is this possible? Is this not contradictory?

Yes, it is! I am a living example!

I served the regular compulsory-military service in the German army in the early 1980s (while it was still West Germany), but I applied and became an officially recognized conscientious objector not very long after I completed my military service. 

My rational mind fully understands and supports the necessity to be able to defend a liberal and humanist constitution based on division of power and democracy with military means when attacked by a hostile military force.

My strong pacifist conviction requires non-violence at all times. Self defense is an exception.