Protector Sentinel

Protector Sentinels are Forerunner machines similar in design and purpose to Sentinels.

Overview
Protector Sentinels are smaller, faster, and occupy less of the population limit. It is in the support role that they excel - their Y-button ability is to attach themselves to one of the player's other units, following it in action. Only one can be attached to a single unit one time.

For the most part, they must be purchased from a Protector Plant.

Variations
There are three different variants of the Protector Sentinels:
 * Offensive Protector - when attached, it attacks units near its host with a pulse of laser fire.
 * Shield Protector - projects a rechargeable energy shield around its host unit.
 * Healing Protector - recharges its host's health when out of combat.

Offensive Protector
The Offensive Protectors are the only Protectors that can be used as a standard unit, because they can attack without being assigned to a squad. In direct combat, they are less effective than standard Sentinels. However, similar to the Sentinel Majors, they are equipped with onboard beam weapons which fires a single blue colored pulse beam at a time. They are of similar shape to the Super Sentinel, but are slightly bigger than Constructors. They have several laser target systems that scan for any threats. Offensive Protectors are the only Variant used in Campaign.

Healing and Shield Protector
The Healing Protectors and the Shield Protectors are the about the same size as Offensive protectors, smaller than a standard Sentinel but larger than a Constructor. Unlike the Offensive Protectors, both variants do not possess guiding lasers. The Healing Protectors and the Shield Protectors are identical in shape; Healing Protectors differs from Shield Protectors as they radiate a green aura. Shield Protectors have the ability to form a protective shield around its host, similar to the Halo 3's Bubble Shield whereas Healing Protectors have the same ability as the UNSC Marines with the Medic Upgrade, meaning they heal the squad after combat.

Spartan and Regret uses
Unlike most units which are limited to only one Protector Sentinel, Spartans and the Prophet of Regret are able to receive multiple Protector Sentinels assigned to them due to their "special units" feature.


 * Prophet of Regret: Upgrading the Prophet of Regret with Ancestral Perversion will give him with two Offensive Protectors for his personal protection.


 * Spartans: There are two methods of getting two Protectors assigned to a Spartan where the Spartan has to hijack a vehicle:
 * The Spartan and one of your vehicles must acquire a Protector assigned to them. Order your Spartan to commandeer your vehicle. This only works when it is your vehicle as when you hijack an enemy vehicle, the vehicle's Protector will be destroyed in the hijacking process.
 * The Spartan must have an assigned Protector. The Spartan then hijacks an enemy vehicle or commandeer a friendly vehicle. After commandeering a vehicle, assign another Protector to the vehicle. If that vehicle is destroyed, the Spartan would still eject as normal, but will have two Protectors assigned to them instead of one.

Wraith and Locust uses
Wraiths and Locusts have the opportunity of multiple shields because they have shields and assigning a Shield Protector would give them a second one.


 * Wraiths: They require the Heavy shield upgrade for this trick to work.


 * Locusts: They have shields by default, you don't need an upgrade. It's very helpful for the Locust because they can still have a shield when they use the Overdrive ability.

Trivia

 * Players can purchase them inside the Protector Plant found on the map Labyrinth.
 * If a unit is being airlifted by the Transport power, the protector unit will follow the pelican, providing it with its capabilities, until the Pelican reaches its destination, which it goes back to the original unit.
 * Offensive Protectors are the only variant to appear in Campaign, Ensemble Studios possibly had ideas to add the other variants but due to balance issues. The other ones would have been set to protect other Sentinels, but it would affect the gameplay and render them harmless.