Mass Effect & Mass Effect 2
The Alliance uses a modified version of the ranking system that has been used for hundreds of years. Soldiers are classified into rank-and-file enlisted personnel, experienced non-commissioned officers (NCOs), and specially trained officers.
The divide between naval personnel and ground forces ('marines') is small. Ground units are a specialized branch of the fleet, just as fighter squadrons are. This unity of command is imposed by the futility of fighting without control of orbit; without the navy, any army is pointless. The marines, as a matter of pride, maintain some of their traditional rank titles; for example, marines have Privates and Corporals instead of Servicemen.
In ascending order of responsibility, the ranks of Alliance are:
Serviceman 3rd Class / Private 2nd Class
Serviceman 2nd Class / Private 1st Class
Serviceman 1st Class / Corporal
Captain / Major
Rear Admiral / General