Sentinel manufacturing facility

A Sentinel Constructor Factory is a massive floating platform that produces Sentinel, Sentinel Major and Enforcer automatons.

Introduction
These facilities float high above the ground to keep them somewhat safe from the majority of Flood if there is ever an outbreak.

On the planet Onyx there was a Sentinel Production Factory which constructed Onyx Sentinels. It was later destroyed by the Spartan-IIs and -IIIs.

Appearance
During Halo 2, they first appear in the level Sacred Icon when the Arbiter reaches the inner side of the Sentinel Wall.

There is an opening in the structure that is similar to the opening where he first entered from the Phantom.

In the distance, above the Library, there are two large floating objects. Once the Arbiter exits the wall, one of these objects is hit with a massive plasma mortar (possibly fired from the Flood to slow down the Forerunner defenses) from presumably a captured Wraith Tank and crashes down to the ground.

In the next level, you spy the same crashed structure being pounded by Wraiths and Scorpions and fight through it as Sentinels and Flood fight each other.

While the appearance inside the structure is badly damaged, some believe it to be a futuristic assembly line, allowing the Monitor to have endless waves of Sentinels to control Flood outbreaks.