From Halopedia, the Halo wiki
Shortly following the Battle of Miridem in 2544, the ship was sent by the ONI to retrieve Doctor Catherine Halsey from a Covenant fleet trapped in a stellar magnetic field that prevented them from jumping into slipspace. Onboard, there were five Spartan-IIs who were eventually sent out to retrieve it using OF92-EVA Booster Frames stored onboard the stealth ship. After the Spartans successfully retrieved the package and the Covenant fleet jumped away, the stealth ship de-cloaked and destroyed the remaining Seraph fighters. After picking the Spartans up, the ship re-cloaked.
In a Q&A for Halo Legends in 2009, Frank O'Connor stated that the ship is not a prowler when questioned about its sophisticated mode of stealth compared to typical UNSC prowlers. This claim has seemingly been ignored in later fiction; not only was the ship's hull classification symbol established to be "PRO-49776" in the Adjunct content of the 2010 release of Halo: The Fall of Reach, with "PRO" being suggestive of "Prowler", but the Sahara-class prowlers such as the UNSC Aladdin in Spartan Ops were depicted as identical to the PRO-49776 in terms of design. Furthermore, Halo Mythos revealed the hull classification symbol of another heavy prowler, UNSC Port Stanley, as "PRO-46328", which uses the same format as "PRO-49776", leaving little doubt as to the nature of the vessel.
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