From Halopedia, the Halo wiki
This warship is approximately two kilometers long and one kilometer wide. The super-destroyer is equipped with enough weapons and firepower to destroy most United Nations Space Command fleets from long range. It is larger than most Covenant warships, even surpassing the keel length of the CCS-class battlecruiser, but itself is dwarfed by the Covenant assault carrier and supercarrier.
The super-destroyer's hull is composed of five bulbous sections - a swollen prow, two lateral lobes, a dorsal bulb and a protruding stern. The ship itself is a pale shade of purple. It is one of the largest ships in the Covenant fleet, being between a battlecruiser and an assault carrier in size. It is armed with energy projectors, along with pulse laser turrets and plasma torpedo batteries found on most Covenant warships.
Though most of its power is likely used up by its large number of weapons, the ship can project a shield strong enough to protect it from multiple nuclear missiles and MAC rounds. However, the shield and hull will buckle under concentrated fire, as occurred when the twenty-seven ships left in Cole's fleet were able to destroy one.
A super-destroyer was encountered by the Colonial Military Administration's Battle Group 4 during its investigation of Harvest in July 2525; the CMA frigates Arabia and Vostok were destroyed after a minute-long skirmish, while the destroyer Heracles was heavily damaged and was forced to retreat. Vice Admiral Preston Cole's forces later encountered the same vessel during the Second Battle of Harvest in March 2526. It single-handedly destroyed thirteen ships in Cole's battle group before being destroyed by concentrated fire.
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