Battle of New Harmony
From Halopedia, the Halo wiki
The Battle of New Harmony was an engagement between UNSC and Covenant forces around the UNSC colony world of New Harmony. During the battle, a prowler, the Razor's Edge, managed to attatch a telemetry probe to a retreating Covenant frigate, allowing it to track the ship and locate K7-49. This subsequently led to Operation: PROMETHEUS.