Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
Commissioned officers, which are distinguished from other officers by their commission, or formal written authority, have ranks that are subdivided into general officers, field-grade officers, and company-grade officers. Warrant officers provide leadership and training in specialized fields and skills. Enlisted Marines with paygrades of E-4 and E-5 are non-commissioned officers (NCOs) while those at E-6 and higher are staff noncommissioned officers (SNCOs). The E-8 and E-9 levels each have two ranks per pay grade, each with different responsibilities. Gunnery sergeants (E-7) indicate on their annual evaluations (called "fitness reports") their preferred promotional track: master sergeant or first sergeant.
Warrant officers provide leadership and training in specialized fields and skills. Unlike other nation's militaries (which rank warrant officers as SNCO equivalents), the United States Military confers warrants and commissions on its warrant officers and classifies them into a separate category senior to all enlisted grades of rank (including officer candidates), cadets, and midshipmen. Because warrant officers are officer-level technical specialists, they generally do not exercise command outside of their specialty. Warrant officers come primarily from the SNCO ranks.
A chief warrant officer, CWO2–CWO5, serving in the MOS 0306 "Infantry Weapons Officer" is often referred to as "Marine gunner," which does not replace his rank. A Marine gunner replaces the chief warrant officer insignia on the left collar with a bursting bomb insignia. Other warrant officers are sometimes incorrectly referred to as "gunner".
Enlisted Marines with paygrades of E-4 and E-5 are non-commissioned officers (NCOs) while those at E-6 and higher are staff noncommissioned officers (SNCOs). The E-8 and E-9 levels each have two ranks per pay grade, each with different responsibilities. Gunnery sergeants (E-7) indicate on their annual evaluations (called "fitness reports") their preferred promotional track: master sergeant or first sergeant. The first sergeant and sergeant major ranks are command-oriented senior enlisted advisors, with Marines of these ranks serving as the senior enlisted Marines in a unit, charged to assist the commanding officer in matters of discipline, administration, and the morale and welfare of the unit. Master sergeants and master gunnery sergeants provide technical leadership as occupational specialists in their specific MOS. First sergeants typically serve as the senior enlisted Marine in a company, battery, or other unit at a similar echelon, while sergeants major serve the same role in battalions, squadrons, or larger units.
The Sergeant Major of the Marine Corps is a billet and with it carries a special rank insignia, conferred on the senior enlisted Marine of the entire Marine Corps, personally selected by the Commandant of the Marine Corps. It, the recently created position of the Senior Enlisted Advisor to the Chairman and the Marine gunner are the only billets which rate modified rank insignia in place of the traditional rank insignia.
Different styles of rank insignia are worn on different Marine uniforms:
Gold stripes on a red flash are worn on the Dress Blue uniform coat. Green stripes on a red flash are worn on the Service uniform coat. Rank insignia are worn on the upper sleeve of both coats. Khaki uniform shirts use green stripes on a khaki flash and are worn on the upper sleeves of both long and short-sleeved shirts. Utility uniform rank insignia are black metal pins and are worn on the collars, or black embroidered insignia sewn into patches of material when wearing armor. Musicians in the United States Marine Band wear insignia with lyre in the center as opposed to the crossed rifles, to denote their lack of a combat mission; full-service Marines who are attached to the 10 field bands of the Operating Forces and Supporting Establishment continue to wear their normal rank insignia. The crossed M1 rifles insignia were added to E-3 through E-8 chevrons in 1959.
No universal insignia for officer candidate rank No official insignia and not currently listed by the Army as an obtainable rank. John J. Pershing's GAS insignia: (collar) (epaulettes) These ranks are reserved for wartime use only, and are still listed as ranks within their respective services Grade is authorized by the U.S. Code for use but has not been created Grade has never been created or authorized
For the Army and Air Force, first sergeants are temporary and lateral ranks and are senior to their non-diamond counterparts, while Marine Corps first sergeants have no lateral movement within paygrade and is a permanent rank.
The rank insignia is used by other Coast Guard senior enlisted leaders.