Study Hard
You’ve got it all wrong if you thought that training and accreditation cease when you step off the ship. When sailors are not on duty, performing drills, or standing watch, they put their time to good use by learning new professional skills and qualifications.
They are not only learning about their sector and job while on the submarine but also preparing for what is to come. For them to be thoroughly knowledgeable when they reach their destination, the crew needs to learn about each individual piece of equipment aboard- which can number in the thousands.