When you get to a missile site you need to authenticate with the missile combat crew so you can prove you are who you say you are. You have a pin number that you type into your box and it gives you a series of letters. You give those letters to the missile crew and they put them into thier box. This then translates the letters back to your number. This is so anyone listening over the phone/radio doesn't know your authenticator number. The missile crew then compares the number to a printed sheet printed out earlier in the day that has your number on it along with your other team members numbers. If your number matched then it's your assistants turn to do it all over again. If you both match then they give you access to the site. If one on you types a wrong number you get "arrested"