They are a BATTALION COMMAND SERGEANT MAJOR
I've seen some sections and squadrons, made up mostly of Officers, that have only a small handful of enlisted personnel and have a full-time 1st Sergeant. Some of the sections may have a Senior-enlisted member, Master Sergeant or above acting as a temporary First Sergeant.
A sergeant is an enlisted soldier higher in rank than a corporal or private, lower than such ranks as staff sergeant and first sergeant. In the U.S. Army a sergeant has pay grade E-5 and wears three stripes.
Where a sergeant fits in the chain of command depends on his rank, since there are several levels of sergeants. Sergeant (SGT) - probably team leader Staff Sergeant (SSG) - probably squad leader Sergeant First Class (SFC) - probably platoon leader First Sergeant (1SG) - probably company First Sergeant Command Sergeant Major (CSM) - probably battalion CSM Sergeant Major of the Army (SMA) - The top enlisted person in the US Army
If the recruiter is an active duty US Marine he can become any grade that he earns through hard work, recommendations from a commanding officer and length of service time. Marines start as private, pfc, lance corporal, corporal, sergeant, staff sergeant and then gunnery sergeant. And finally the highest ranks of enlisted men the Master Sergeant and First Sergeant
Private (E1) = PVTPrivate (E2) = PV2Private First Class (E3) = PFCSpecialist (E4) = SPC (formerly SP4)Corporal (E4) = CPLSergeant (E5) = SGTStaff Sergeant (E6) = SSGSergeant First Class (E7) = SFCMaster Sergeant (E8) = MSGFirst Sergeant (E8) = 1SGSergeant Major (E9) = SGMCommand Sergeant Major (E9) = CSMSergeant Major of the Army (E9) = SMA
A Senior Master Sergeant is ranked above a Master Sergeant in the United States Air Force and the United States Space Force. It is the eighth enlisted rank in the Air Force and the Space Force, equivalent to a First Sergeant in the Army and Marine Corps or a Senior Chief Petty Officer in the Navy and Coast Guard.
US Army: 2nd Lieutenant is 2LT, 1st Lieutenant is 1LT, Captain is CPT, Major is MAJ, Lieutenant Colonel is LTC, Brigader General is BGN, General is GEN. Private is PVT, Private First Class is PFC, Corporal is CPL, Sergeant is SGT, Staff Sergeant is SSG, Sergeant First Class is SFC, Master Sergeant is MSG, First Sergeant is 1SG.
In the US Army, the next rank above Staff Sergeant would be Sergeant First Class, followed by Master Sergeant and First Sergeant (both grade E8), then by Sergeant Major and Command Sergeant Major (both grade E9). Sergeant Major of the Army is the seniormost noncommissioned officer rank in the US Army. In the US Marine Corps, the next rank above Staff Sergeant (E6) would be Gunnery Sergeant (E7), followed by Master Sergeant and First Sergeant (E8), Master Gunnery Sergeant and Sergeant Major (E9), then Sergeant Major of the Marine Corps. Unlike other military branches of the US Armed Forces, where Staff Sergeant is pay grade E6, Staff Sergeant in the Air Force is pay grade E5 - equivalent to a Sergeant in the Army or Marine Corps. It is followed by Technical Sergeant (E6), Master Sergeant (E7), Senior Master Sergeant (E8), Chief Master Sergeant and Command Chief Master Sergeant (E9), and, finally, Chief Master Sergeant of the Air Force, who - like the Sergeant Major of the Army and the Sergeant Major of the Marine Corps - is the most senior noncommissioned officer in the entire branch. The British, Commonwealth, and some European forces end their enlisted ranks at Staff Sergeant (or equivalent), and rate enlisted personnel senior to Staff/Colour Sergeants as Warrant Officers.
There is no such rank as "First Class Sergeant". You have either Sergeant First Class, which is E7, or First Sergeant, which, along with Master Sergeant, is E8.
In the United States Marine Corps, a Master Sergeant is colloquially referred to as "Top" as a term of respect and endearment. The nickname originated from the military tradition of addressing senior enlisted personnel by the term "Top" as a sign of their authority and experience. It is a way for junior Marines to show deference and acknowledge the Master Sergeant's leadership role within the unit.
Officers outrank enlisted personnel. Thus, a Second Lieutenant - which is 01 - outranks an E6 in any branch of service, whether Navy (Petty Officer First Class), Coast Guard (same rank as Navy), Army (Staff Sergeant), Marine Corps (Staff Sergeant), or Air Force (Technical Sergeant).