A reference to "Starfleet Marine Corps" appears on the briefing chart in TUC, which seems to suggest that an organisation somewhat based on the old US/UK traditions of the Marines exists in the Trek 'Verse, which is fair enough as this should be the case.
However, on reflection I think that most of the limited evidence argues against the SMC being a seperate service (which seems to be the most common fanon notion):
1) West (first name possibly Patrick) wore a regular Starfleet uniform (in Command White rather than the dark blue worn by combat specialists in TFF) with the insignia of a Vice Admiral, perhaps suggesting that "Colonel" is the title given to SMC (sub-brigade level) 'field commanders' (company commander would be "Major") suggesting that he is part of the regular Chain of Command as does -
2) The fact that they are called the Starfleet Marine Corps, rather than the Federation Marine Corps, placing them as subordinate to Starfleet (Command) rather than being equals as fanon often (though not always) has it.
Rather, I think that the "Starfleet Marine Corps" is more likely to be the 'shorthand' for the corps-size 'polar operations (and general maritime activites)' unit within either Starfleet Special Operations (SSO or SSOCOM) or Starfleet Search and Rescue (perhaps Specialist Hazard Action and Rescue Command (SHARC)?), possibly based on Andor, with 'desert warfare' units (Vulcan?) and 'cultural observation and recon' units (Earth?) existing in parallel as part of the same command.
The SMC and 'desert warfare' units would therefore be more comparable to DEVGRU/Delta Force (in the SSOCOM role) or USAF PJs (in the CSAR role) and the 'cultural observation and recon' units would evoke Force Recon and possibly elements of the Army Green Berets.
It's not a common idea, but I don't think there's anything to contradict it?
However, on reflection I think that most of the limited evidence argues against the SMC being a seperate service (which seems to be the most common fanon notion):
1) West (first name possibly Patrick) wore a regular Starfleet uniform (in Command White rather than the dark blue worn by combat specialists in TFF) with the insignia of a Vice Admiral, perhaps suggesting that "Colonel" is the title given to SMC (sub-brigade level) 'field commanders' (company commander would be "Major") suggesting that he is part of the regular Chain of Command as does -
2) The fact that they are called the Starfleet Marine Corps, rather than the Federation Marine Corps, placing them as subordinate to Starfleet (Command) rather than being equals as fanon often (though not always) has it.
Rather, I think that the "Starfleet Marine Corps" is more likely to be the 'shorthand' for the corps-size 'polar operations (and general maritime activites)' unit within either Starfleet Special Operations (SSO or SSOCOM) or Starfleet Search and Rescue (perhaps Specialist Hazard Action and Rescue Command (SHARC)?), possibly based on Andor, with 'desert warfare' units (Vulcan?) and 'cultural observation and recon' units (Earth?) existing in parallel as part of the same command.
The SMC and 'desert warfare' units would therefore be more comparable to DEVGRU/Delta Force (in the SSOCOM role) or USAF PJs (in the CSAR role) and the 'cultural observation and recon' units would evoke Force Recon and possibly elements of the Army Green Berets.
It's not a common idea, but I don't think there's anything to contradict it?