Enlisted Marine Corps ranks are broken down into three levels, Junior Enlisted, Non-Commissioned Officers, and Staff Non-Commissioned Officers. As a Marine moves up the ladder his or her responsibility and contribution to the mission increases.
Also, children born abroad to two non-citizen nationals or to one alien parent and one non-citizen national parent are eligible for non-citizen national status. This is so rare that the State Department does not even issue a certificate for it. Non-citizen nationals are delineated as such in their passports.
Permanent residents must present their I-551 Permanent Resident Card when entering the United States. A passport is not required to enter the US, but you may need one to enter Mexico, depending on your nationality. A passport is the best form of international identification and having one may help you avoid hassles when crossing borders.