In the two pilots, security officers are seen wearing blue (rather than TOS red) and having a unique never seen again blocky 'C'-shaped insignia (different from the more curved 'Enginneering' symbol worn during TOS. This is often dismissed as 'Early Installment Weirdness' or an out-and-out costuming error however the second point especially makes this unlikely to me.
For most of the Star Trek franchise, security guards have been shown as either part of Operations/Engineering (ENT, TOS, TNG, VOY), usually combined with Tactical (ENT, TNG, VOY) but not always (TOS) or even a separate service of their own (ENT's MACOs) and while the latter somewhat reflects the RW USN relationship between GMs & MAA's (rare outside of major capital ships) IIRC, the fandom/licencees don't seem to find this satisfactory given the profusion (even before ENT IFAIK?) of 'Starfleet Marines' and similar organisations.
Now personally, I think that especially in the TNG+ era the basic logistics argue against the idea of having a 'dedicated infantry' Division of Starfleet/Federation Uniformed Services, so I think that most of the 'Ship's Security' contingent are likely to be either unrated 'crewman' or specialists in other field (Communications, Engineering and Armory are intuitable based on canon), but I think it's also possible that (in a more realistic enlisted heavy setting?) that the bulk of the section are actually part of the Science Division (possibly designated Landing Party Specialists? Somewhat 'Hollywood CSIs' or somewhat like an Science version of the Religious Program Specialist of the US Armed Forces?)
I'm also relatively keen on the idea of a Starfleet Intelligence or Federation Security Agency representive being embarked onboard as a 'big picture'/'impartial observer' on the Senior Staff (analogous to the NCIS Agent-Afloat Program rather than the old Soviet 'Political Officers') who would also be in charge of managing any 'high-risk' planned security operations and risk assessments, but with the actual 'Team Leader' role going to senior enlisted or junior uniformed officers.
Shamrock Holmes
For most of the Star Trek franchise, security guards have been shown as either part of Operations/Engineering (ENT, TOS, TNG, VOY), usually combined with Tactical (ENT, TNG, VOY) but not always (TOS) or even a separate service of their own (ENT's MACOs) and while the latter somewhat reflects the RW USN relationship between GMs & MAA's (rare outside of major capital ships) IIRC, the fandom/licencees don't seem to find this satisfactory given the profusion (even before ENT IFAIK?) of 'Starfleet Marines' and similar organisations.
Now personally, I think that especially in the TNG+ era the basic logistics argue against the idea of having a 'dedicated infantry' Division of Starfleet/Federation Uniformed Services, so I think that most of the 'Ship's Security' contingent are likely to be either unrated 'crewman' or specialists in other field (Communications, Engineering and Armory are intuitable based on canon), but I think it's also possible that (in a more realistic enlisted heavy setting?) that the bulk of the section are actually part of the Science Division (possibly designated Landing Party Specialists? Somewhat 'Hollywood CSIs' or somewhat like an Science version of the Religious Program Specialist of the US Armed Forces?)
I'm also relatively keen on the idea of a Starfleet Intelligence or Federation Security Agency representive being embarked onboard as a 'big picture'/'impartial observer' on the Senior Staff (analogous to the NCIS Agent-Afloat Program rather than the old Soviet 'Political Officers') who would also be in charge of managing any 'high-risk' planned security operations and risk assessments, but with the actual 'Team Leader' role going to senior enlisted or junior uniformed officers.
Shamrock Holmes