A ballistics expert is a person who specializes or has a good deal of knowledge about the ballistics. Now, ballistics is the concept of the flight, launch and mechanics of the firing of any projectile in the atmosphere. Thus, in order to know the accuracy of the rocket in hitting its target, a ballistics expert will be helpful in determining it.
I would say an unreliable narrator because that kind of narrator is the best at keeping secrets from the reader. If that's not an option, then a restricted narrator because they only know a limited amount of information.
