Battlegroup Stalingrad was a nine-ship United Nations Space Command naval taskforce in 2552 under the command of Admiral Carl "Buster" Patterson. Their objective was to exfiltrate Dr. Halsey and a joint unit of SPARTAN-IIs and SPARTAN-IIIs that were stuck on the planet of Onyx, as well as to gather supposed Forerunner technologies on the planet that might turn the tide of war for the UNSC. However, they engaged a superior Covenant fleet in orbit, in what devolved into the Battle of Onyx.
However, eventually, the Covenant destroyed all of Battlegroup Stalingrad except for the stealthed Prowler UNSC Dusk.