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The UNSC Belleisle is an auxiliary ship at the service of the UNSC Navy after the Human-Covenant War.
Not much is known about the Belleisle, except for that it was present along with the UNSC Dunedin, UNSC Port Stanley and UNSC Glamorgan when ONI Research Facility Trevelyan was brought into real space from slipspace.
The UNSC Belleisle was likely named in reference to several Royal Navy ships of the same name or to those ships' namesake, the island of Belle-Île.