Battle of EarthEdit
- Main article: Battle of Earth
Harper was most likely part of the Orbital Defense Grid over Africa, in charge of protecting the MAC orbital platform clusters in that region, which included Cairo Station. Fleet Admiral Harper was not seen on screen, however he was heard in two separate transmissions regarding the attack on Earth by the Prophet of Regret's battle group (consisting of 15 Covenant Capital Ships: 13 CCS-class battlecruisers and 2 CAS-class assault carriers). Harper's transmissions were as follows:
- Fleet Admiral Harper: "This is Fleet Admiral Harper, we are engaging the enemy!"
- Fleet Admiral Hood: "Negative Admiral. Form a defensive perimeter around the cluster."
- Fleet Admiral Harper: "First echelon, you're with me. Blanket those cruisers. Take 'em out one by one. Second echelon, keep those carriers busy."
- Fleet Admiral Harper: "The carriers are breaking through sir, they're heading straight for the Cairo!"
- Fleet Admiral Hood: "Cortana, concentrate your fire on the first carrier. Admiral, do what you can against the second."
His voice in the transmissions sounded young for the high rank of Fleet Admiral. The readout from Cairo Station showed that Harper's fleet consisted of 8 cruisers and 67 frigates, as well as a large number of fighter units, as at one point he ordered his GA-TL1 Longsword-class Interceptors to blanket the Covenant cruisers and take them out, one by one.
Presumably, he continued to fight in the late Battle of Earth, during the Covenant Loyalist invasion.
Though he has the same rank as Fleet Admiral Hood, Harper is his subordinate. This is due to the fact that as the Chief of Naval Operations, Hood is the highest-ranking officer in the UNSC Navy.