The 55th Mechanized Brigade, a unit composed of 9,216 clone troopers and additional support staff, functioned as a mechanized infantry brigade within a corps of the Grand Army of the Republic during the Clone Wars. This conflict pitted the Galactic Republic against the Confederacy of Independent Systems. A senior clone commander oversaw the brigade, and one of its clone trooper lieutenants, who became the camp commander of the Republic Detention Center on the Core Worlds planet Anaxes, specifically in its capital city of Pols Anaxes, after sustaining an injury that caused him to walk with a noticeable stiffness. In approximately 19 BBY, the 55th Mechanized Brigade's lieutenant encountered Bardan Jusik, a Mandalorian Force-sensitive individual posing as an inmate, along with three former Republic clone troopers disguised as regular clones: Fi, Spar, and Sull. They sought to liberate Ruusaan Skirata, the daughter of the Mandalorian mercenary Kal Skirata, who was imprisoned there. After approving their deceptive request to release the prisoner, the lieutenant directed the four individuals to the Hut Eight Bravo detention block, the location where Ruusaan was being held.
The 55th Mechanized Brigade made its debut in Order 66: A Republic Commando Novel, a novel authored by Karen Traviss and released in 2008.