Sharpfin-class escort corvette
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By the modern standards of the early/mid-2500s, the Sharpfin-class was considered under armed and slow. Because of this, they were rarely employed for even routine tasks like planetary customs patrols.
In 2526, on the planet, Netherop, John-117 brokered a deal with the leaders of the Castoffs, Samson and Roselle. In exchange for the the Castoffs' cooperation and assistance in dealing with the Covenant forces on the planet, the UNSC would provide them with one of these corvettes as well as a ride to a planet of their choosing. Admiral Michael Stanforth was hesitant to lend this corvette to the Castoffs due to their wish to retreat to the Insurrectionist world of Gao, though was eventually persuaded to do so by John-117.
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