From Halopedia, the Halo wiki
On November 2, 2552, RECON 127 was deployed from the UNSC In Amber Clad shortly after the frigate arrived at Installation 05 in the Coelest system. The unit was intended to study a large structure buried under one of the installation’s many islands. Upon arrival, RECON 127 was attacked by Covenant forces and their Albatross was shot down.
The members of RECON 127 did not survive the following ground engagement. However, the unit was able to transmit a series of scans of the site to the In Amber Clad. The information the team gathered from the site revealed that it was the remains of a long-dormant Forerunner vessel that had been carefully hidden below the island circa 97,445 BCE.
All that remained of RECON 127 was the evidence of the battle on the Island, with RECON 127's Albatross's wreckage and matériel spilling in the wind.