At present, we have a small company of NPC marines.
Do you think you can lead them to peace and prosperity?
Can you keep DS5 safe from those that wish it harm?

If the answer is yes, then sign on the dotted line and give your soul to a station that needs your help.
There are a number of positions available for Marines, especially Fighter Pilots and a Marine officers.

As this is an enlisted position, you do not need to enter the Cadet academy, but you need to follow a chain of command, which is headed by the stations CO. That said, it is still highly recommended that you enrol in the Academy to gain a grounding in how the OF works. This wold be decided upon mainly by you and the CO.

And so many more.