From Halopedia, the Halo wiki
The Brigantine is an ancient heavy carrier class, designed by the Sangheili prior to the establishment of the Covenant. Centuries after being rendered obsolete as a mainline warship within the Covenant fleet, Brigantines were placed in Covenant missionary and tithe fleets throughout a majority of the empire's existence. Following the Covenant's fall during the Great Schism, Brigantines have since been brought back into service as a command ship by Sangheili factions during the Blooding Years, primarily the Swords of Sanghelios and Jul 'Mdama's Covenant. These ships have since then been upgraded to modern specifications.
While "brigantine" referred to a sail configuration, rather than a specific ship class, they were often more powerful, faster and more agile than smaller ships, such as schooners or sloops, but smaller than the brigs used by naval forces, and frequently found use as pirate ships, fleet suppliers and light escorts.
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