(covers information from several alternate timelines)
The rank system used by the United Earth MACO military force of 22nd century, and the Terran Empire in the mirror universe, were based on traditional army and naval ranks from Earth's past. In this case, the precedent for MACO ranks was most likely the Marine Corps, since Starfleet itself is based on a naval motif.
The flag officer rank of general was used by General Casey, commanding officer of the MACOs who were assigned to the Enterprise NX-01. This rank was approximately equivalent to an Starfleet admiral. (ENT: "The Expanse")
The rank of major was used by MACO field officers commanding a squad of soldiers on special assignments. The insignia was a gold oak leaf on a yellow shoulder patch. The oak leaf insignia appears to have been carried over from the US insignia for major.
Major J. Hayes commanded the MACOs aboard Enterprise. Traditionally, a major was equivalent of a naval lieutenant commander. However, Starfleet had no such rank at the time. Though Hayes may have technically outranked Lieutenant Malcolm Reed, the MACO team was still subordinate to the ship's chief of security. (ENT: "The Xindi")
The sergeant insignia consisted of three white chevrons on a blue shoulder patch.
- N. Kemper was a MACO sergeant assigned to Enterprise.
- Travis Mayweather was a MACO sergeant assigned to the ISS Enterprise.
The corporal insignia consisted of two white chevrons on a blue shoulder patch.
Several corporals were seen assigned to Enterprise, and also posted at other Starfleet assignments.
The private insignia consisted of a single white chevron on a blue shoulder patch.
|Enlisted personnel||Commissioned officers||Generals and flag officers|
|ENS||LT JG||LT||LT CMDR||CMDR||CAPT||FCAPT||CDORE||RADM||VADM||ADM||FADM|
|2nd LT||1st LT||CAPT||MAJ||LT COL||COL||BRIG||MAJ GEN||LT GEN||GEN||MARSHAL|
|Positions:||Boatswain • Chief • Corpsman • Engineer's mate • Specialist • Technician • Yeoman||TAC • SO • 3rd • 2nd • 1st • CO • DD||Portmaster • Chief of Staff • CinC|
|Services:|| Andorian • Bajoran • Cardassian • Ferengi • Jem'Hadar • Klingon • Romulan • SS • United Earth MACO • United Earth/Federation Starfleet • United States • Vulcan|
Mirror universe: Terran Empire Starfleet • Terran Empire MACO
The MACOs appear to have followed the same basic rank system of Earth armies, with American-style insignia. The producers and writers of Star Trek: Enterprise apparently avoided the army ranks that sounded naval (lieutenant, captain, etc.) to avoid confusion.