All Marines are required to go through Recruit Training and School of Infantry. By completion of School of Infantry, all Marines should hold at least the rank of E2.
Promotions passed E2 are all ability and performance based. As you continue learning and increasing your ability to perform as well as excel, you will begin progress until you hit E4. Once a Marine hits E4, they are required to take the Corporals Leadership Course.
Upon hitting E5, you are required to take your Basic Leadership Course. At E6 you are required to take Senior Leadership Course. Everything after E6 is position based, and first come first serve. Those that have been in the unit longer will be promoted once a position becomes available.
All positions are selected by the person with the next closest rank for promotion with the points, badges, qualifications, and service history to be a suitable non-commissioned officer.
Once you are an NCO (E5 - E9) you can qualify for a commission.