Sentinel Major

Sentinel Majors are artificial levitating constructs designed by the Forerunners and serve on the Halo Installations. They are upgraded versions of regular Sentinels, possessing golden armor and deadlier blue Sentinel Beams.

Introduction
They are similar to a regular Sentinel, in basic shape and function. Sentinel Majors, however, have gold armor, instead silver, have stronger blue beams rather than weaker orange beams, are protected by a light energy shield, and fire more accurately. They were only observed on Installation 05 during the Battle of the Quarantine Zone. In the game, they are seen combating Flood and the Covenant.

Sentinels have been known to have been created long before Alpha Halo 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.

In gameplay, they are often seen hovering around Enforcers whenever the Arbiter combats them. In addition, they rarely travel by themselves; instead, they travel in packs of 3-5, as well as "commanding" normal Sentinels.

Function
The Sentinels are the defenders of the 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 and in small quantity. 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. It is also possible that there must be a massive outbreak, like the one seen on Installation 05, to give reason enough to construct these stronger versions.

In combat, their shields are less powerful than that of an Elite's, and the beam fired is blue instead of orange-red. It is also more powerful, but its battery drains faster as a result. You can pick up this beam and the normal beam as your primary and secondary weapons. One can tell the difference between the weapons simply by noting that the stronger of the two is gold in color, rather than silver.

Rarely, they can also be seen fixing pieces of Forerunner material, much like the Constructors do. However, this is extremely rare, and they cannot fix anything, even in groups, for massive-scale damage/repair.

Tactics
Individually, their relatively low shielding (As compared to an Elite, for instance) is made up by their maneuverability. As with Rangers, they can easily slice through the air, evading slow-moving projectiles (Such as Rockets) and coerce the combatant to concentrate on one at a time. The best weapon for them is the Covenant Carbine or the Plasma Rifle. First, the Covenant Carbine has a pretty strong punch and can penetrate the shielding in one or two shots. Then, in an additional two shots, the Major will go down. For the Plasma Rifle, you will rely upon it's steady rate of fire to wear down the shields rather than take it out decisively. Shotguns can also be effective if the target is at close range. When facing these worthy opponents, be certain to have some cover within close proximity-these as these Sentinels travel in groups, and can take your shielding out in seconds. Behind cover, use hit-and-run tactics to evade fire. Be sure to take one out at a time, as a wasted effort will be useless - the shielding will still be there, and you will have to take it out all over again. Once you have taken out the Sentinel, however, you can have the extremely powerful laser. This can take out the "legs" of an Enforcer in less than five seconds, whilst an ordinary Sentinel Beam takes over double the time. If your shields are down and you are out in the open, crouch (Or do something to evade fire quickly) and then activate your active camouflage. Use this time to duck behind cover and do not fire in this duration.

Trivia

 * When a Sentinel Major's Sentinel Beam is dropped it takes the color of an average Sentinel Beam. When picked up, however, the color is gold like a Sentinel Major and the beam is blue.
 * The Sentinel Majors don't appear in Halo 3, because a Flood outbreak would be very unlikely on Installation 00, due to the fact that the Forerunners had made "protective measures" against the Flood, also, Gravemind did not know Earth's location until the first human hosts were infected on Installation 04.
 * A single overcharged Plasma Pistol bolt is sufficient enough to take out a Sentinel Majors shield and destroy the Sentinel all in one shot.
 * Through the use of modding the map file of the map Quarantine Zone in Halo 2, you will find that there are three types of Sentinels, one being the normal "Grey Sentinel", one being a "Grey Sentinel with shielding", and the last being the "Golden Sentinel" also with shielding.
 * The Sentinel Major beam does not appear in Multiplayer.
 * While in Halo 2, the Major Sentinel's blue beamed weapon is stronger than the standard one, the similar blue beam of the Auto-Turret in Halo 3 is strangely weaker than the standard Sentinel Beam.
 * There is an Easter Egg in Halo 2 where a Sentinel Major will have a Needler instead of the Blue Sentinel Beam.