From Halopedia, the Halo wiki
The ship was originally a peacekeeping ship in service with the Colonial Military Administration. Prior to 2525, Kronstadt had been retired for decades. With the dawn of the Human-Covenant War, the UNSC retrieved the vessel from storage and retrofitted it into a warship for service in the conflict against the Covenant.
During or after 2540, it deployed a squad of Orbital Drop Shock Troopers and a SPARTAN-II commando, Cal-141, via SOEIV to the Covenant-occupied planet Heian. The commando team infiltrated a former alien settlement, where they engaged several Unggoy and a Jiralhanae chieftain before assassinating a Covenant Prophet. After the mission, which resulted in the deaths of the Spartan and one ODST, the vessel retrieved the survivors.
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