Military units in the context of "Armed force"

Combat arms (or fighting arms in non-American parlance) are troops within national armed forces who participate in direct tactical ground combat. In general, they are units that carry or employ weapons, such as infantry, cavalry, and artillery units. The use of multiple combat arms in mutually supporting ways is known as combined arms. In some armies, notably the British Army and Canadian Army, artillery and combat engineer units are categorized as combat support, while in others, such as the U.S. Army, they are considered part of the combat arms. Armored troops constitute a combat arm in name, although many have histories derived from cavalry units.

Artillery is included as a combat arm primarily based on the history of employing cannons in close combat, and later in the anti-tank role until the advent of anti-tank guided missiles. The inclusion of special forces in some armed forces as a separate combat arm is often doctrinal because the troops of special forces units are essentially specialized infantry, often with historical links to ordinary light infantry units.

Barrier troops, blocking units, or anti-retreat forces are military units that are located in the rear or on the front line (behind the main forces) to maintain military discipline, prevent the flight of servicemen from the battlefield, capture spies, saboteurs and deserters, and return troops who flee from the battlefield or lag behind their units. Barrier troops differ from military police, as barrier troops exert their effect through physical presence near specific allied units, as a preventative measure against retreat and other actions, whereas military police apprehend and control those who have already done so, typically in a wider area.

A military staff or general staff (also referred to as army staff, navy staff, or air staff within the individual services) is a group of officers, enlisted, and civilian staff who serve the commander of a division or other large military unit in their command and control role through planning, analysis, and information gathering, as well as by relaying, coordinating, and supervising the execution of their plans and orders, especially in case of multiple simultaneous and rapidly changing complex operations. They are organised into functional groups such as administration, logistics, operations, intelligence, training, etc. They provide multi-directional flow of information between a commanding officer, subordinate military units and other stakeholders. A centralised general staff results in tighter top-down control but requires larger staff at headquarters (HQ) and reduces accuracy of orientation of field operations, whereas a decentralised general staff results in enhanced situational focus, personal initiative, speed of localised action, OODA loop, and improved accuracy of orientation.

A commander "commands" through their personal authority, decision-making and leadership, and uses general staff to exercise the "control" on their behalf in a large unit. Most NATO nations, including the United States and most European nations, use the Continental Staff System which has origin in Napoleon's military. The Commonwealth Staff System, used by most of the Commonwealth, has its origin in the British military.