Apply for ROTC scholarship in high school. Go for a very long and detailed interview. Find out a month or two later that you are accepted. Also get accepted to college. Do 4 years worth of ROTC classes and leadership labs in college. Graduate with a reasonably good gpa. Get selected for navigator training. Go to navigator training for a year and a half. Then on to primary weapons system training for 6 months. Then squadron training for another few months. Then presto! You're a navigator.