First you must be qualified to perform that job. You may have had training on how to do it else where, but not on a sub or in particular, this submarine. You must qualify or re-qualify on the boat. In a commissioned vessal you are given a year to accomplish this. In new construction it's a bit harder to do in that time frame since you need to wait until the system you want to qualify on is installed.
Every person has to know a certain level of basics to be trusted to sail and operate on a sub.
This is necessary because you never know where you might be when an emergency occures and be required to assist in damage control or other emergency procedures. You might be the ONLY person in a space and solving the problem quickly will mean saving your life and every one elses. Each system and compartment required 3 levels of testing to become qualified on or in it. So, grab your flashlight. Get your systems drawings and qual book from the C.O.B. and come crawl through a year of little or no sleep.