Combat support

In the United States Army, the term combat support refers to units that provide fire support and operational assistance to combat elements. Combat support units provide specialized support functions to combat units in the areas of chemical warfare, combat engineering, intelligence, security, and communications.

Combat support should not be confused with combat service support, which are units which primarily provide logistical support by providing supply, maintenance, transportation, health services, and other services required by the soldiers of combat units to continue their missions in combat. Expressed another way, Combat Support units are focused on providing operational support to combat units, while Combat Service Support units are focused on providing logistical support to combat units. Actual combat units are collectively referred to as combat arms units; hence, all army units fall into the category of either combat arms, combat support, or combat service support.

Currently, U.S. Army organizational doctrine uses the classification "Maneuver, Fires and Effects" (MFE) and "Operations Support" (OS) to group the former combat support arms branches into Maneuver Support; Special Operations Forces; Network and Space Operations; and Intelligence, Surveillance, and Reconnaissance functional areas.

Within the U.S. Army, the traditional combat support branches are/were:

Before the Army ceased using the combat arms / combat support arms / combat service support arms classification system in 2008, the following branches were classified as combat support arms from the year designated.

United States Marine Corps doctrine designates all Ground Combat Element (GCE) forces, other than infantry, including field artillery, assault amphibian, combat engineer, light armored reconnaissance, reconnaissance, and tank as combat support. The primary mission of all USMC combat support units is to directly support the infantry.

...
Wikipedia