From Halopedia, the Halo wiki
One of the testers was Frederic-104, with his suit having a primary purpose to serve as a testbed for new technologies before they were incorporated into the MJOLNIR (GEN2) platform, a more modern armor that would later be utilized by Spartan-IVs.
Spartan Frederic-104 received a prototype Centurion armor upon upgrading to the Mark VI platform at his return to Earth in October 2552, shortly before the Battle for Earth. With it, Frederic fought numerous battles on Earth, and later participated in the Onyx Conflict. Following his return to Earth in 2553, he continued to field-test multiple variants of the Centurion armor during highly confidential operations, until at least October 2558.
The GEN2 variant is equipped with C4I2SR (Command, Control, Communications, Computers, Intelligence, Information, Surveillance, and Reconnaissance) technology which, combined with the warfighting skills of the Spartan wearer, has had major ramifications on UNSC doctrine on battlespace shaping and operations planning. The suit's threat management system also features the latest situational awareness tactical software and cognition-enhancing neural interlinks.
The GEN2 variant was still being developed by the Watershed Division.
By 2558, a GEN2 variant of Centurion is in use by Spartan Fred-104.
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