A battlegroup (British/Commonwealth term), or task force (U.S. term) in modern military theory is the basic building block of an army's fighting force. A battlegroup is formed around an infantry battalion or armoured regiment, which is usually commanded by a lieutenant colonel. The battalion or regiment also provides the command and staff element of a battlegroup, which is complemented with an appropriate mix of armor, infantry, and support personnel and weaponry relevant to the task it is expected to perform.