The Sentinel droid series, alternatively called the war-droid or military droid series, represents the sole identified line of androids utilized as war machines by both the Galactic Republic and the Sith Empire during the time of the Jedi Civil War. This series included variants such as the Mark I, Mark II, Mark III, Mark IV, and Mark V, all of which shared an identical external appearance. The design and structural framework of the HK-series were derived from this Sentinel line.
A KT-400 military droid carrier unloads Sentinel droids on Onderon
During the period of the Mandalorian Wars, the Republic forces under the command of Revan utilized these droids, deploying them from KT-400 military droid carriers. The droids were controlled remotely from these carriers, a method reminiscent of the Droid Control Ships employed by the Trade Federation and the Confederacy of Independent Systems thousands of years later. These droids saw action during the Republic's conquest of the Mandalorian remnants on Dxun. One such carrier suffered a crash landing on Dxun, and both the carrier and its contingent of droids were later discovered by the Jedi Exile.
Sentinel droids were armed with blaster rifles and could be augmented with personal energy shields. Unlike the spherical shields used by other droid models, these shields allowed the Sentinel droids to maintain mobility while shielded.
The Ahto City Civil Authority made extensive use of these droids for maintaining security and for the apprehension of lawbreakers within Ahto City. Revan himself was captured on Manaan by a force of sentinel droids commanded by a Selkath officer. The Selkath, known for their pacifistic nature, favored the sentinel droid, much like the Mark IV assault droid, over using organic soldiers.
Certain individuals, including Ahlan Matale and Nurik Sandral, employed these droids in the role of personal bodyguards.