The Colonial Marine Corps
The CMC is the space-borne military of Earth. Though still smaller than their MarSec counterparts, the CMC is noted for very fast capital ships and fierce defense of Earth property.
Like Earth itself, little is known of the CMC’s structure or hierarchy. Unfortunately (or possibly by design) most opinions of them are colored by Delta Green, a fictional Cortex series featuring an elite squad of marines who are among the few to know of and defend against a secret alien invasion of the solar system.