Gunny

Gunnery Sergeant (abbrev: Gunny) is an enlisted title within the Royal Manticoran Marine Corps. It holds no military paygrade, a Gunny is the right hand of the supervising Marine officer. A Gunny is the senior Non-Commisioned Officer (NCO) and part of the leadership triad (commanding officer, executive officer, senior NCO). A Gunny can be any Marine who has become an NCO, but is normally a First Sergeant.

Honorverse

In "Filed of Dishonor" (HH4 - Chapter 15) David Weber explains how the honorary title of Gunny came to the Marine Corps. “"Well, well! If it isn't Gunny Babcock," Ramirez said, and the woman smiled at him. The Royal Manticoran Marines no longer used the official rank of gunnery sergeant. They'd lost it when they merged with the Royal Army three hundred T-years before and hadn't reinstated it when they split back off a hundred years after that. But the senior Marine noncom aboard any ship was still referred to as "gunny," and Iris Babcock had been the battalion sergeant-major attached to HMS Fearless with Ramirez and Hibson.”

TRMN

The First Sergeants usually hold the position of Gunny in a MarDet.

Gunnery Sergeant Rank insignia - Royal Manticoran Marine Corps
Corporal	Platoon Sergeant	Staff Sergeant	Master Sergeant	First Sergeant	Sergeant Major