Sentinel Major
From Halopedia, the Halo wiki
Sentinel Majors are the same basic design as the Sentinel, with two notable exceptions. One is the gold-colored armor plating replacing the normal silver-colored armor plating. Whether this is simply a color difference or a different armor alloy altogether is unknown. The second difference is that the Sentinel Majors are armed with Advanced Sentinel Beams that fire blue-colored lasers instead of the weaker orange-colored beams that normal Sentinels use. The Sentinel Major is also equipped with energy shielding that can absorb more damage than a normal Sentinel.
Template:SentinelSentinel Majors are artificial flying constructs designed by the Forerunners and serve on the Halo Installations. They are similar to a regular sentinel, but are gold in color, have stronger beams, are protected by a light energy shield, and fire more accurately. They were only observed on Installation 05.
Sentinels have been known to have been created long before Installation 04 was ever conceived. They operated automated facilities such as Gas Mines like the one found on Threshold for "untold centuries" before the facility was redesigned to research the Flood. Therefore it is possible that they were only outfitted for combat after the Flood was discovered.
The Sentinels are the "police" of the Halo installations, and are controlled by the Monitor of the Installation. Their primary purpose is to contain small outbreaks of Flood, however they can only manage flood for a short time. Should an outbreak grow beyond the sentinels' ability to control, Enforcers and Sentinel Majors are activated by the Monitor of the Installation to assist the Sentinels.
Trivia
Though in Halo 2 only the Sentinel Majors have shields, in the Halo levels, Two Betrayals and The Maw, A few Sentinel Minors have shields.
