For operational tasks the most common unit is the battlegroup, formed around a combat unit and supported by units (or sub-units) from other areas. An example of a battlegroup in the Reactive Force (e.g. the 1st Brigade) would be two companies of armoured infantry (e.g. from the 1st Battalion of the Mercian Regiment), one squadron of heavy armour (e.g. A Squadron of the Royal Tank Regiment), a company of engineers (e.g. B Company of the 22nd Engineer Regiment), a battery of artillery (e.g. D Battery of the 1st Regiment of the Royal Horse Artillery) and smaller attachments from medical, logistic and intelligence units. Typically organised and commanded by a battlegroup headquarters and named after the unit which provided the most combat units, in this example it would be the 1 Mercian Battlegroup). This creates a self-sustaining mixed formation of armour, infantry, artillery, engineers and support units, typically 600 to 1,000 soldiers commanded by a lieutenant colonel. The table below demonstrates how three or four battlegroups make up a brigade and three or four brigades make up a division. A division is currently the largest unit the British Army is capable of deploying independently, although it could be grouped with three or four other divisions from a multi-national coalition to form a corps.