SUMMARY
The Mission to Cleyell was a UNSC mission to the colony world of Cleyell, which had recently been glassed by a fringe group of Covenant remnants sometime in 2556. The UNSC Cascadia was sent to investigate after detecting a distress signal coming from the surface of Cleyell, and deployed a team of ODSTs, including Holly Tanaka, to look for survivors. During the search, the team came across a group of hostile Kig-Yar, and after fighting them off, discovered a group of survivors hiding in the caves of the planet. The team was able to rescue all survivors without taking casualties.
RELATED MEDIA
These events are depicted in the comic Halo: Escalation Volume 3, which was the subject of a Halo Book Club on September 6th, 2016.