Operation Thresher
From FreeSpace Wiki
Operation Thresher was a failed operation executed in Antares. Losses on the Terran side at 504 pilots dead, and also had 14 pilots status MIA. However, it did cut off supply lines to Vasuda Prime.
Operation Thresher took place right before the main Descent: FreeSpace campaign and is only mentioned in the first command briefing. No details are known about the nature of the operation.