The Requiem Campaign was a UNSC mission to return to Requiem, and take control of the shield world away from Jul 'Mdama and his Covenant remnants in February 2558, six months after the Battle of Requiem. The campaign was led by the UNSC Infinity, along with a large contingent of Spartan-IV fireteams and several science teams specialized in Forerunner technology. While the Infinity quickly won orbital superiority around Requiem, Covenant ground forces put up a strong defense, including using the shield world's Promethean soldiers against the UNSC. Both sides fought fiercely for control of the world and the Forerunner artifacts contained within, culminating in the discovery of the Janus Key, a Forerunner device that revealed the locations of all other Forerunner artifacts. While the Janus Key was initially discovered by Catherine Halsey under command of Jul 'Mdama, a resulting firefight resulted in each of two halves of the key falling into UNSC and Covenant control. Not realizing that he only had half of the Janus Key, however, Jul 'Mdama ordered Requiem be sent into the system's star. Both the Covenant and UNSC forces managed to escape prior to Requiem's destruction, each with one half of the key.
These events are depicted in the video game Halo 4.