First Sergeant

First Sergeant is the name of a military rank used in many countries, typically a senior non-commissioned officer.

United States Army
In the United States Army, the rank of First Sergeant (abbreviated 1SG) is above the rank of Sergeant First Class and below the rank of Sergeant Major. It is equal in grade to Master Sergeant, although the two ranks have different responsibilities. The rank is abbreviated as "1SG" in the Army. Master sergeants are laterally promoted to first sergeant upon selection by the senior leadership at a battalion or higher level, depending on available billets and opportunities. Upon reassignment to a non-first sergeant billet, the soldier reverts back to their original rank of master sergeant. First sergeants are generally the senior non-commissioned officers of company (battery, troop) sized units, and are unofficially but commonly referred to as "first shirt", "top", "top sergeant", "top soldier", "top kick", or "top hat", due to their seniority and their position at the top of the company's enlisted ranks. They are sometimes referred to as "second hat" because the Company Commander may entrust them with important responsibilities, even over one of the company's lieutenants.

First Sergeants handle the leadership and professional development of their soldiers, manage the promotable soldiers within the company, and are the first step in an Article 15 (non-judicial punishment) proceeding, as well as the daily responsibilities of running the company/unit.

Until September 1942, First Sergeant was a Grade 2 enlisted rank, equivalent to Technical Sergeant; it was then elevated to Grade 1, equivalent to Master Sergeant.