What is the designation for the rank that wears 3 chevrons above 1 diamond above 3 rockers?

The rank designated by 3 chevrons above 1 diamond above 3 rockers is known as First Sergeant (1stSgt). In the U.S. Marine Corps, the chevrons represent the rank of Sergeant, and the diamond indicates the position of First Sergeant, which is a leadership role within a unit. This rank is specifically associated with the responsibility for the enlisted personnel within the unit and acts as a liaison between the officers and the enlisted ranks.

The chevron and rocker insignia signifies a higher grade than regular Sergeant ranks, emphasizing the additional responsibilities and authority of the First Sergeant role. This rank is crucial in maintaining good order and discipline among the enlisted ranks as well as providing guidance and mentorship to junior Marines.