After graduating USMMA?

[beyond]

Graduate as a commissioned officer, Ensign for Navy/Coast Guard and 2nd Lieutenant for Air Force/Marines/Army

[pointguard]

that its not automatic to be Commissioned into those Branches as AD upon USMMA Graduation, or is it just that you won't get to automatically pick what you'd like to do when you go there? How is it decided who gets certain spots, Class Rank? Thank you.