I would suggest you explore the available commercial diving schools, and discern whether you are able to complete a course. The idea that the Navy may train you is not a sure thing. You may commit to the Navy for a duration of years, from which you can not extract yourself, with no guarantee you will ever become a diver. Their diving courses are tough, thorough and entensive. If you should not be selected or qualify, what will you do with the rest of your commitment? As a Vietnam veteran, allow me to assure you there are no guarantees concerning what you want, versus what the particular service believes their needs to be.