From Halopedia, the Halo wiki
The UNSC Agincourt was a frigate in operation in the early 2550's. In October 2552, it was sent to planet Onyx to offload supplies at Camp Currahee for the incoming candidates for the new SPARTAN-IIIs, Delta Company. As they were leaving, the Camp Commandant, Lieutenant Commander Kurt Ambrose asked for observational assistance from the craft after hearing strange sounds coming from Zone 67. However, the Agincourt was discovered and was destroyed by a swarm of Onyx Sentinels that had been activated within Onyx.
The vessel is likely named for the Battle of Agincourt, a battle between the English and French during the Hundred Years' war.
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