Operation: REAR GUARD was a defensive operation conducted by the United Nations Space Command and Alliance of Sangheili Clans, occurring on May 8, 2553 in orbit of Earth. ONI intelligence suggested that a True Covenant fleet, under the command of Brute High Chieftain Thietus, would attempt to fully subjugate Earth and gain access to The Ark. The operation saw over two hundred UNSC and sixty Sangheili Defence Force vessels converge on Earth to participate in its defence, including dozens of orbital defence platforms and newly deployed Bulwark defensive satellites. The larger True Covenant fleet initially gained the upper hand and pressed dangerously close to Earth itself; however, timely intervention by thirty two Theran and Ve'nek vessels, arriving from through The Portal, turned the tide