From Halopedia, the Halo wiki
The Lursu-pattern brigantine entered service in the Former Age; the earliest centuries of Sangheili space travel prior to contact with the San'Shyuum at Ulgethon. Following the end of the War of Beginnings, the San'Shyuum aimed to diminish Sangheili shipbuilding capability and thus reduced the brigantine's role to one of mere formality. 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 - with the former posessing the majority of surviving brigantines. Many of these ships were sourced from ancient orbital shipbreaking facilities and upgraded to modern specifications, pressed into service as a heavy carrier.
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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