Applied at the recruiting office and took the ASVAB exam. Score requirements changes year to year depending on the needs of the navy but for Nuke it is around 75-99. While at boot-camp, there is a tiny interview process where 3 Navy personnel tell you what the big three rates are like (roughly) for ET, EM, and MM and you write down in order of preference what you would like to be rated as. After that, they go into an office to deliberate and once they come out your fate is determined and you are now rated as one of the three.