Headquarters and Service Company

A Headquarters and Service Company is a company sized military unit, found at the battalion level and higher in the United States Marine Corps. In identifying a specific headquarters unit, it is usually referred to by its abbreviation as H&S. While a line company is formed of three or four platoons, H&S is made up of the headquarters staff and headquarters support personnel of a battalion, MEU, regiment, MEB, division, or MEF. As these personnel do not fall inside one of the line companies of the battalion, regiment, or division, the H&S Unit is the unit to which they are administratively assigned. The typical personnel strength of an average H&S Company for a Marine infantry battalion is 270 personnel.

Inside a battalion H&S, the headquarters staff will usually include the following key officers and primary staff officers:

Depending on the unit, extra support officers will round out the staff, including one or two Navy Medical officer(s),  Career Planner, Judge Advocate, and a  Navy Chaplain (often collectively referred to as the "special staff"), as well as essential Navy and Marine Corps non-commissioned officers and enlisted support personnel in the occupational specialities of the executive staff sections (S1 through S4 and the S6), and a battalion sergeant major, who is principal advisor to the battalion commander on matters regarding enlisted personnel. Additionally, H&S will contain further personnel assigned to support and sustain the mission of the battalion headquarters, including maintenance and motor transport, field mess, and supply.

H&S itself will be commanded by a company commander (usually a captain) who is supported by a company executive officer (usually a first lieutenant) and a company first sergeant. All personnel in H&S fall under the administrative command of the H&S company commander, but in practice, the primary and special staff officers report directly to the battalion commander, and while the battalion commander is administratively assigned to H&S, he or she is the H&S company commander's higher commander and thus the H&S company commander operationally answers directly to the battalion commander. The mission of the H&S company commander is to run the administrative and Marine training aspects of H&S, and to support the battalion primary staff by facilitating the environment in which they operate and in turn support the battalion commander in commanding the battalion.

At the regimental and division level, H&S is similarly constituted of the regimental or division commander, his or her staff, and the support elements, but the ranks of the staff and support personnel are typically greater to reflect the greater level of responsibility at higher echelon units. However, the company commander of a regimental H&S is usually still a captain. A division H&S is usually a battalion in itself and is commanded by a lieutenant colonel.

In keeping with the long standing practice of referring to company sized artillery units as "batteries" the headquarters company element of an artillery battalion or higher is referred as a Headquarters and Service Battery. Additionally, some high level headquarters elements for special units are not company sized and are referred to as "detachments;" as a result, these units are formally referred to as Headquarters and Service Detachments.