Cradle
From Halopedia, the Halo wiki
Summary
Cradle was a refit station capable of intersystem travel. It was a square kilometer in diameter, and capable of refitting six destroyers, three from her upper surface and three from her lower surface, in a matter of hours.
In 2552, it was present at the Battle of Sigma Octanus IV. The ship was used as a shield for the fleet when the Covenant attacked, and it was sacrificed so that the humans could protect their ships from a salvo of plasma fire.