Space Marines are organised into Chapters, autonomous armies which retain their own heraldry, fleet and distinct identity. Chapters typically contain about a thousand Space Marines plus an unspecific number of Initiates, support staff, and Adeptus Mechanicus maintenance units. The majority of Chapters follow the organizational structure detailed in the fictional version of the Codex Adeptus Astartes. Each Chapter is arranged into ten Companies of one hundred marines each, led by a captain. The First Company of a Chapter is usually composed of veterans, privileged with suits of Terminator Armour, and the Tenth Company is almost always formed by newly recruited marines serving as Scouts. The Second to Fifth are the Battle Companies, typically consisting of six Tactical Squads, two Assault Squads, and two Devastator Squads. The Sixth to Ninth are Reserve Companies; Sixth and Seventh contain all Tactical Squads, while Eighth are entirely Assault and Ninth are all Devastator.